qcow2: Plug memory leak on qcow2_invalidate_cache() error paths

Introduced in commit 5a8a30d.  Spotted by Coverity.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/qcow2.c

@@ -1308,6 +1308,7 @@ static void qcow2_invalidate_cache(BlockDriverState *bs, Error **errp)
     options = qdict_clone_shallow(bs->options);
 
     ret = qcow2_open(bs, options, flags, &local_err);
+    QDECREF(options);
     if (local_err) {
         error_setg(errp, "Could not reopen qcow2 layer: %s",
                    error_get_pretty(local_err));
@@ -1318,8 +1319,6 @@ static void qcow2_invalidate_cache(BlockDriverState *bs, Error **errp)
         return;
     }
 
-    QDECREF(options);
-
     if (crypt_method) {
         s->crypt_method = crypt_method;
         memcpy(&s->aes_encrypt_key, &aes_encrypt_key, sizeof(aes_encrypt_key));