domain_event.c: don't deref NULL on an OOM error path

* src/conf/domain_event.c (virDomainEventGraphicsNewFromDom):
Return NULL when handling out-of-memory error, rather than
falling through with ev=NULL and then assigning to ev->member.
(virDomainEventGraphicsNewFromObj): Likewise.

src/conf/domain_event.c

@@ -687,7 +687,7 @@ virDomainEventPtr virDomainEventGraphicsNewFromDom(virDomainPtr dom,
         ev->data.graphics.phase = phase;
         if (!(ev->data.graphics.authScheme = strdup(authScheme))) {
             virDomainEventFree(ev);
-            ev = NULL;
+            return NULL;
         }
         ev->data.graphics.local = local;
         ev->data.graphics.remote = remote;
@@ -712,7 +712,7 @@ virDomainEventPtr virDomainEventGraphicsNewFromObj(virDomainObjPtr obj,
         ev->data.graphics.phase = phase;
         if (!(ev->data.graphics.authScheme = strdup(authScheme))) {
             virDomainEventFree(ev);
-            ev = NULL;
+            return NULL;
         }
         ev->data.graphics.local = local;
         ev->data.graphics.remote = remote;