Avoid crash on OOM in virportallocatortest

The virportallocatortest did not check if the object
allocation failed in all cases. This lead to a crash
on OOM in the testsuite
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

tests/virportallocatortest.c

@@ -67,6 +67,9 @@ static int testAllocAll(const void *args ATTRIBUTE_UNUSED)
     int ret = -1;
     unsigned short p1, p2, p3, p4, p5, p6, p7;
 
+    if (!alloc)
+        return -1;
+
     if (virPortAllocatorAcquire(alloc, &p1) < 0)
         goto cleanup;
     if (p1 != 5901) {
@@ -137,6 +140,9 @@ static int testAllocReuse(const void *args ATTRIBUTE_UNUSED)
     int ret = -1;
     unsigned short p1, p2, p3, p4;
 
+    if (!alloc)
+        return -1;
+
     if (virPortAllocatorAcquire(alloc, &p1) < 0)
         goto cleanup;
     if (p1 != 5901) {