block: Assert validity of BdrvActionOps In qmp_transaction, assert that the BdrvActionOps to be used is actually valid. This assertion failing is very improbable, however, it might happen, if a new TransactionActionKind is introduced "out of order" and the actions[] array is not updated. Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>