mgcp_client_init(): consider "talloc returns NULL" case

Change-Id: I131019b3c04a7860a118991c8f3bb31185fb11e4
diff --git a/src/libosmo-mgcp-client/mgcp_client.c b/src/libosmo-mgcp-client/mgcp_client.c
index 819461d..eeb5e4f 100644
--- a/src/libosmo-mgcp-client/mgcp_client.c
+++ b/src/libosmo-mgcp-client/mgcp_client.c
@@ -735,6 +735,8 @@
 	struct mgcp_client *mgcp;
 
 	mgcp = talloc_zero(ctx, struct mgcp_client);
+	if (!mgcp)
+		return NULL;
 
 	INIT_LLIST_HEAD(&mgcp->responses_pending);
 	INIT_LLIST_HEAD(&mgcp->inuse_endpoints);