block: remove redundant check before g_slist_find()

An empty GSList is represented by a NULL pointer, therefore it's a
perfectly valid argument for g_slist_find() and there's no need to
make any additional check.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-id: 1435583533-5758-1-git-send-email-berto@igalia.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/io.c

@@ -283,7 +283,7 @@ void bdrv_drain_all(void)
         }
         aio_context_release(aio_context);
 
-        if (!aio_ctxs || !g_slist_find(aio_ctxs, aio_context)) {
+        if (!g_slist_find(aio_ctxs, aio_context)) {
             aio_ctxs = g_slist_prepend(aio_ctxs, aio_context);
         }
     }