Fix DaemonProcess launch uncaught exception when the executable path is invalid/non-executable

[egasato]

I've fixed the bug before reading the Contributing Guidelines, so if any changes must be made do not hesitate to tell me. Given that this Pull Request is to fix a bug I've run into, I will describe it as if I were opening an Issue (if you need me to create an actual Issue I can do so as well). Also, because I am unexperienced regarding the macOS ecosystem, I will not upload the crash report because I don't know which segments might contain private information (if they are needed, which is unlikely due to the simplicity of the bug, I can share them privately).

What happened

• I expected the Syncthing GUI app to start, the tray icon to appear, and the daemon to be launched.
• The tray icon did not show up or it did briefly and disappeared quickly; the daemon was not running in any case.

What operating system, operating system version and version of Syncthing you are running

• Model: MacBook Air 2022
• Chip: Apple M2
• OS: macOS Sequoia 15.3.1 (24D70)
• Syncthing: 1.29.2-1 (102900201)

The same for other connected devices, where relevant

• Not relevant.

Screenshot if the issue concerns something visible in the GUI

• Not relevant.

Console log entries, where possible and relevant

• Not shared due to privacy concerns (and ignorance about the personal information it has).

[egasato]

I forgot to add that I ran into this problem when I migrated my Homebrew installation from an external drive (symlink) to the internal drive. Uninstalling and installing, as well as reinstalling, did not solve this issue because the configuration files (e.g. the plist file that contains the NSUserDefaults data) were not deleted in the process.

I added a log to print the path of the executable being used because I consider too cumbersome to look for the (potentially many) configuration files where that information might be stored.