block/block-copy: block_copy_dirty_clusters: fix failure check

ret may be > 0 on success path at this point. Fix assertion, which may
crash currently.

Fixes: 4ce5dd3e
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20200526181347.489557-1-vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/block-copy.c

@@ -622,8 +622,10 @@ out:
          * block_copy_task_run. If it fails, it means some task already failed
          * for real reason, let's return first failure.
          * Still, assert that we don't rewrite failure by success.
+         *
+         * Note: ret may be positive here because of block-status result.
          */
-        assert(ret == 0 || aio_task_pool_status(aio) < 0);
+        assert(ret >= 0 || aio_task_pool_status(aio) < 0);
         ret = aio_task_pool_status(aio);
 
         aio_task_pool_free(aio);