inspector: fix crash caused by uninitialized GVariant
we were not checking the return gboolean of
gtk_action_muxer_query_action() which was
returning FALSE
for the crash case, meaning
it didn't set the passed in GVariant
, but
we were still using it as it was non-null.
We make a simple fix by initializing the
GVariant
to NULL which covers the mentioned case.
Fixes #5729 (closed)