Bug: Activating the app from its URI/CLI sometimes causes a crash

### Description

When activating the app via an invalid protocol, for example `files-dev://` or `files-dev:test`, the app does one of two things:
- if the app is already open, it crashes completely
- if the app is not open, it will open to the splash screen and hang indefinitely

### Steps To Reproduce

1. Opened the Run dialogue box via Win+R
2. Entered an (invalid) app protocol URI, e.g. `files-dev:test`
3. Observed the behaviour as described in the **'Description'** section of the issue

### Files Version

[`0b8e0af`](https://github.com/files-community/Files/commit/0b8e0af88e54db295b5320bfb6deb4335a088629)

### Windows Version

10.0.26200.8875

### User ID

_No response_

### Log File

[debug.log](https://github.com/user-attachments/files/30163928/debug.log)

Reproduce the issue with files-dev:// or files-dev:test from the Windows Run dialog, both while Files is open and after it is closed. Start by examining the linked debug.log and the app's URI/CLI activation path. Done means invalid protocol input no longer crashes an open app or leaves a newly launched app hanging on the splash screen.

Written by the indexing model from the issue text.