[Bug Report] ffmpeg & ffprobe not used if libwebp support is not available

[honeybeaver]

Describe the bug

On the current development build (v0.25.1-26-g22d14fd8), with the changes to ffmpeg & ffprobe handling (#4688 ?), stash does not use ffmpeg & ffprobe available in $PATH, if libwebp support is not available. Prior builds did, and on Apple Silicon, builds from Homebrew and MacPorts are not compiled with libwebp support. Builds from https://evermeet.cx/ffmpeg/ are not native Apple Silicon builds either, and they also do not appear to have libwebp support either. Scanning and other key functions are non functional due to this, as Stash behaves as if there is no ffmpeg & ffprobe available. Users should not need to do a custom compile of ffmpeg & ffprobe.

To Reproduce
Steps to reproduce the behavior:

1. Update to v0.25.1-26-g22d14fd8 on an Apple Silicon machine
2. Run scan (which fails with error missing ffmpeg and/or ffprobe)
3. Or, manually enter ffmpeg & ffprobe paths (which are not accepted with error: invalid ffmpeg path: ffmpeg is missing libwebp support)

Expected behavior
Stash runs like prior builds using ffmpeg without libwebp support.

Screenshots
n/a

Stash Version: (from Settings -> About): 0.25.1-26-g22d14fd8

Desktop (please complete the following information):

• OS: [e.g. iOS] macOS 14.4.1, Apple Silicon
• Browser [e.g. chrome, safari] any browser
• Version [e.g. 22] any browaer

Smartphone (please complete the following information):

• Device: [e.g. iPhone6] n/a
• OS: [e.g. iOS8.1] n/a
• Browser [e.g. stock browser, safari] n/a
• Version [e.g. 22] n/a

Additional context
n/a

[WithoutPants]

Thanks for the report of this regression. #4852 should address this issue.