block: Fix Transaction leak in bdrv_root_attach_child()

The error path needs to call tran_finalize(), too.

Fixes: CID 1452773
Fixes: 548a74c
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20210503110555.24001-2-kwolf@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -2916,13 +2916,14 @@ BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
                                    child_role, perm, shared_perm, opaque,
                                    &child, tran, errp);
     if (ret < 0) {
-        bdrv_unref(child_bs);
-        return NULL;
+        assert(child == NULL);
+        goto out;
     }
 
     ret = bdrv_refresh_perms(child_bs, errp);
-    tran_finalize(tran, ret);
 
+out:
+    tran_finalize(tran, ret);
     bdrv_unref(child_bs);
     return child;
 }