Error saving screenshots on macOS

Description

On a macOS (15.0.1, arm64), building from Xcode, I am getting an error (on screen) whenever trying to save screenshots.

Expected behavior

Expected the screenshot to be saved to a PNG file successfully.

Actual behavior

I occasionally get an error and the screenshot isn't saved.

Steps to reproduce the bug

1. Open Retroarch
2. Open a GBA rom
3. Open mGBA
4. Click Command -> Take Screenshot
5. See the error pop up

Bisect Results

I don't know what this means, but I was messing with the code anyway, so here's what I found.

While investigating the error I added a few printf's to debug it, and after that a few screenshots were successfully saved in weirdly named directories:

'/Users/vini/Library/Containers/com.libretro.dist.RetroArch/Data/`64o
/Pokemon - LeafGreen Version (USA, Europe) (Rev 1)-241115-151226.png'
'/Users/vini/Library/Containers/com.libretro.dist.RetroArch/Data/`v]o
/Pokemon - LeafGreen Version (USA, Europe) (Rev 1)-241115-150716.png'
'/Users/vini/Library/Containers/com.libretro.dist.RetroArch/Data/`vqo
/Pokemon - LeafGreen Version (USA, Europe) (Rev 1)-241115-150345.png'

Looking at the code, what seems to be happening is:

• screenshot_dump gets called (line 255) with the following arguments:
  • screenshot_dir: ""
  • name_base: /Applications/_Games/Pokemon - LeafGreen Version (USA, Europe) (Rev 1)
  • savestate: 0
  • has_valid_framebuffer: 0
  • fullpath: 0
  • use_thread: 1
• new_screenshot_dir is declared (line 318) but never initialized (so it contains memory trash, I suppose?)
• settings->bools.auto_screenshot_filename is true, so we calculate a new state->shotname (e.g. Pokemon - LeafGreen Version (USA, Europe) (Rev 1)-241115-151226.png).
• We check if new_screenshot_dir is empty in line 377 but it's not (it contains memory trash), and settings->bools.screenshots_in_content_dir is false, so it still hasn't been initialized.
• We create a pathname (line 382) with an uninitialized string but a valid filename, and it only works occasionally (when the uninitialized string happens to be a valid directory name?).

A lot of these are educated guesses, but I thought it'd be better to write it up and maybe help someone actually fix it.

Version/Commit

Commit hash b0da8b15794afbb6df6ae30ede16b1a7423c60e8

Environment information

• OS: macOS (15.0.1, arm64)
• Compiler: Xcode

Start in tasks/task_screenshot.c at the screenshot_dump declaration around line 255 and the new_screenshot_dir declaration around line 318. Trace its use in the path construction around lines 377-382, then reproduce the macOS screenshot flow from the listed steps. Done means screenshots save successfully to the expected PNG location without malformed directories.