Add missing check for OOM with virVMXEscapeHexPipe

The virVMXFormatConfig called virVMXEscapeHexPipe but
forgot to check for OOM. This caused data to silently
be lost.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/vmx/vmx.c

@@ -3096,7 +3096,8 @@ virVMXFormatConfig(virVMXContext *ctx, virDomainXMLOptionPtr xmlopt, virDomainDe
 
     /* def:description -> vmx:annotation */
     if (def->description != NULL) {
-        annotation = virVMXEscapeHexPipe(def->description);
+        if (!(annotation = virVMXEscapeHexPipe(def->description)))
+            goto cleanup;
 
         virBufferAsprintf(&buffer, "annotation = \"%s\"\n", annotation);
     }