uml: Fix umlProcessAutoDestroyDom dom processing

There's no need to check if @dom exists before trying to
call virDomainObjListRemove since it must exist due to
prior checks.

Additionally, if we do remove the @dom, then set it to NULL
so that the virObjectUnlock isn't referencing something that
is deleted.
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>
Reviewed-by: NMarc Hartmayer <mhartmay@linux.vnet.ibm.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>

src/uml/uml_driver.c

@@ -747,8 +747,10 @@ static int umlProcessAutoDestroyDom(void *payload,
                                      VIR_DOMAIN_EVENT_STOPPED,
                                      VIR_DOMAIN_EVENT_STOPPED_DESTROYED);
 
-    if (dom && !dom->persistent)
+    if (!dom->persistent) {
         virDomainObjListRemove(data->driver->domains, dom);
+        dom = NULL;
+    }
 
     if (dom)
         virObjectUnlock(dom);