gdesktopappinfo: Add checks for empty argv

There shouldn’t be any issues here with empty argv arrays since an empty
`Exec=` line is already checked for. Encode that explicitly with an
assertion.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

gio/gdesktopappinfo.c

@@ -1880,6 +1880,10 @@ g_desktop_app_info_load_from_keyfile (GDesktopAppInfo *info,
       else
         {
           char *t;
+
+          /* Since @exec is not an empty string, there must be at least one
+           * argument, so dereferencing argv[0] should return non-NULL. */
+          g_assert (argc > 0);
           t = g_find_program_in_path (argv[0]);
           g_strfreev (argv);