applications: Ignore broken symlinks

We still do need to query mtime from the symlink itself in order to keep
filesystem accounting happy, so wait for ENOENT while doing
g_key_file_load_from_file() in order to figure out we are dealing with
a broken link (or a no longer existing file, which is also possible). This
avoids spewing any warnings with those.

https://bugzilla.gnome.org/show_bug.cgi?id=786132