[BUG] Can't select and apply custom slang shaders.

Description

Hi! I'm unable to select and apply custom slang shaders.

Expected behavior

With a core loaded, when going to Main Menu > Quick Menu > Shaders > Shader #0, navigating to my custom shader file location and selecting my shader file, I should get back to the shader options menu.

Actual behavior

When selecting my custom shader file, a Suggested cores menu appears instead, and my shader is not applied. Trying to do so from the desktop menu crashes RetroArch:

(1)(deck@steamdeck ~)$ flatpak run org.libretro.RetroArch -v
F: Not sharing "/esp" with sandbox: Ignoring blocking autofs path "/esp"
[INFO] [Config]: Looking for config in: "/home/deck/.var/app/org.libretro.RetroArch/config/retroarch/retroarch.cfg".
[INFO] RetroArch 1.16.0 (Git 6c2cc45)
[INFO] === Build =======================================
[INFO] CPU Model Name: AMD Custom APU 0405
[INFO] Capabilities: MMX MMXEXT SSE SSE2 SSE3 SSSE3 SSE4 SSE42 AES AVX AVX2 
[INFO] Version: 1.16.0
[INFO] Git: 6c2cc45
[INFO] Built: Oct 31 2023
[INFO] =================================================
[INFO] [Input]: Found input driver: "x".
[INFO] [Environ]: SET_PIXEL_FORMAT: RGB565.
[INFO] [Core]: Version of libretro API: 1, Compiled against API: 1
[INFO] [Core]: Geometry: 320x240, Aspect: 1.333, FPS: 60.00, Sample rate: 48000.00 Hz.
[INFO] [Audio]: Set audio input rate to: 48000.00 Hz.
[INFO] [Video]: Set video size to: 640x480.
[ERROR] [Wayland]: Failed to connect to Wayland server.
[INFO] [Vulkan]: Vulkan dynamic library loaded.
[INFO] [Vulkan]: Found vulkan context: "vk_x".
[INFO] [Vulkan]: Detecting screen resolution: 2560x2240.
[INFO] [X/Vulkan]: X = 0, Y = 0, W = 640, H = 480.
[INFO] [Vulkan]: Found GPU at index 0: "AMD Custom GPU 0405 (RADV VANGOGH)".
[INFO] [Vulkan]: Found GPU at index 1: "llvmpipe (LLVM 15.0.7, 256 bits)".
[INFO] [Vulkan]: Using GPU index 0.
[INFO] [Vulkan]: Using semaphores for WSI acquire.
[INFO] [Vulkan]: Using GPU: "AMD Custom GPU 0405 (RADV VANGOGH)".
[INFO] [Vulkan]: Queue family 0 supports 1 sub-queues.
[INFO] [Vulkan]: Got 3 swapchain images.
[INFO] [Vulkan]: Using resolution 640x480.
[INFO] [Vulkan]: Using RGB565 format.
[INFO] [Vulkan]: Loading stock shader.
[INFO] [Joypad]: Found joypad driver: "sdl2".
[INFO] [Autoconf]: Steam Virtual Gamepad configured in port 1.
[INFO] [DBus]: Suspended screensaver via DBus.
[INFO] [Video]: Found display server: "x11".
[INFO] [PulseAudio]: Requested 24576 bytes buffer, got 18432.
[INFO] [Audio]: Started synchronous audio driver.
[INFO] [ALSA] Using ALSA version 1.2.7.2
[INFO] [Microphone]: Initialized microphone driver.
[INFO] [Display]: Found display driver: "vulkan".
[INFO] [Playlist]: Loading history file: "/home/deck/.var/app/org.libretro.RetroArch/config/retroarch/content_history.lpl".
[INFO] [Playlist]: Loading history file: "/home/deck/.var/app/org.libretro.RetroArch/config/retroarch/content_music_history.lpl".
[INFO] [Playlist]: Loading history file: "/home/deck/.var/app/org.libretro.RetroArch/config/retroarch/content_video_history.lpl".
[INFO] [Playlist]: Loading history file: "/home/deck/.var/app/org.libretro.RetroArch/config/retroarch/content_image_history.lpl".
[INFO] [Playlist]: Loading favorites file: "/home/deck/.var/app/org.libretro.RetroArch/config/retroarch/content_favorites.lpl".
[INFO] [Autoconf]: Steam Virtual Gamepad configured in port 1.
Qt: Session management error: Could not open network socket
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
kf.solid.backends.udisks2: Failed enumerating UDisks2 objects: "org.freedesktop.DBus.Error.Disconnected" 
 "Not connected to D-Bus server"
[INFO] [Shaders]: Applying shader: "null".
[INFO] [Qt]: Reloading shader parameters.
[INFO] [Qt]: Reloading shader parameters.
malloc(): unaligned tcache chunk detected
(134)(deck@steamdeck ~)$

Steps to reproduce the bug

1. Download this custom shader and drop the file to /home/deck/.var/app/org.libretro.RetroArch/config/retroarch/shaders/.
2. With a core loaded, go to Main Menu > Quick Menu > Shaders > Shader #0, navigate and select the previously downloaded custom shader /home/deck/.var/app/org.libretro.RetroArch/config/retroarch/shaders/sharp-shimmerless.slang, brings a Suggested cores menu.

Notes

• I can successfully select and apply a shader retrieved with the online updater, from the default path that opens up when I select Shader #0.

Version/Commit

• RetroArch: 1.16.0.3, flatpak version.

Environment information

• OS: SteamOS 3.5.7

Start at Main Menu > Quick Menu > Shaders > Shader #0 and reproduce with the supplied sharp-shimmerless.slang file in the Flatpak shader directory. Compare selecting that file with selecting a shader from the online updater's default path; done means the custom shader returns to the shader options menu, applies successfully, and does not open Suggested cores or crash.