entry-directories: skip entries whose desktop file id is not valid UTF-8

[Fantu]

The desktop file id is the entry's path relative to the application directory with the separators turned into dashes, so any byte of the file or directory name that is not valid UTF-8 is handed out as-is by gmenu_tree_entry_get_desktop_file_id().

Introspection bindings refuse to convert such a string. The menu applet reads the id for every entry in appUtils.js loadDirectory(), so a single badly named file anywhere under an applications directory makes cjs throw, the exception propagates out of the applet constructor and the applet is never created — the menu button disappears from the panel entirely:

[menu@cinnamon.org]: String from C value is invalid UTF-8 and cannot be safely stored
[menu@cinnamon.org]: Failed to evaluate 'main' function on applet: menu@cinnamon.org/0
loadDirectory@/usr/share/cinnamon/applets/menu@cinnamon.org/appUtils.js:104:46

Reported as Debian #893510 in 2018 and again as #64 here in 2023.

This validates the id before handing it to the callback and skips the entry when it is not valid UTF-8, logging the offending path so it can be found and renamed. Doing it here rather than at load time also covers the case where the file name is fine but one of the directories leading to it is not — that breaks the applet just the same.

Testing

Tested on Debian unstable with Cinnamon 6.6.9, rebuilding libcinnamon-menu-3-0 6.6.0 with the change. Two cases, a .desktop file with a 0xE9 byte in its name and a correctly named file inside a directory with a 0xE9 byte in its name:

	before	after
either case	menu applet not created, no menu button in the panel	111 apps in 12 categories, same as a healthy system, plus Ignoring "…": its name is not valid UTF-8