Honour error returned by virBitmapFormat

The code formatting NUMA args was ignoring the return value
of virBitmapFormat, so on OOM, it would silently drop the
NUMA cpumask arg.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/qemu/qemu_command.c

@@ -6861,8 +6861,9 @@ qemuBuildNumaArgStr(const virDomainDefPtr def, virCommandPtr cmd)
         virCommandAddArg(cmd, "-numa");
         virBufferAsprintf(&buf, "node,nodeid=%d", def->cpu->cells[i].cellid);
         virBufferAddLit(&buf, ",cpus=");
-        cpumask = virBitmapFormat(def->cpu->cells[i].cpumask);
-        if (cpumask) {
+        if (!(cpumask = virBitmapFormat(def->cpu->cells[i].cpumask)))
+            goto cleanup;
+
         /* Up through qemu 1.4, -numa does not accept a cpus
          * argument any more complex than start-stop.
          *
@@ -6876,7 +6877,6 @@ qemuBuildNumaArgStr(const virDomainDefPtr def, virCommandPtr cmd)
             goto cleanup;
         }
         virBufferAdd(&buf, cpumask, -1);
-        }
         def->cpu->cells[i].mem = VIR_DIV_UP(def->cpu->cells[i].mem,
                                             1024) * 1024;
         virBufferAsprintf(&buf, ",mem=%d", def->cpu->cells[i].mem / 1024);