[PATCH] block: Fix bdrv_activate() not to fail without medium

[Markus Armbruster <armbru@redhat.com>]

bdrv_activate() returns failure without setting an error when
!bs->drv.  This is suspicious.  Turns out it used to succeed then,
until commit 5416645fcf82 changed it to return -ENOMEDIUM.

Return zero instead.

Fixes: 5416645fcf82 (block: return error-code from bdrv_invalidate_cache)
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 block.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 0ece805e41..9855c102de 100644
--- a/block.c
+++ b/block.c
@@ -6860,7 +6860,7 @@ int bdrv_activate(BlockDriverState *bs, Error **errp)
     GRAPH_RDLOCK_GUARD_MAINLOOP();
 
     if (!bs->drv)  {
-        return -ENOMEDIUM;
+        return 0;
     }
 
     QLIST_FOREACH(child, &bs->children, next) {
-- 
2.48.1