block: Simplify bdrv_append_temp_snapshot() logic
Noticed while checking Coccinelle results. Naming a label 'out:'
when it is only used on error paths is weird. Also, we had some
dead stores to 'ret'. Meanwhile we know that snapshot_options
is NULL on success and that QDECREF(NULL) is safe. So merge the
two exit paths into one by careful control over bs_snapshot.
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <
20170427215821.19397-8-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>