tools: Fix handling of empty argv in various minor GLib tools

This won’t really affect anything, but we might as well fix them to not
crash if called with an empty `argv` by someone (ab)using `execve()`.

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

gobject/gobject-query.c

@@ -196,7 +196,7 @@ main (gint   argc,
     }
   
   if (!gen_froots && !gen_tree)
-    return help (argv[i-1]);
+    return help ((argc > 0) ? argv[i-1] : NULL);
   
   if (!indent_inc)
     {