libxl: don't unlock virDomainObj if refcnt is 0

Commit 6472e54a unlocks the virDomainObj even if libxlDomainObjEndJob
returns false, indicating that its refcnt has dropped to 0.
Signed-off-by: NJim Fehlig <jfehlig@suse.com>

src/libxl/libxl_driver.c

@@ -4816,10 +4816,8 @@ libxlDomainMemoryStats(virDomainPtr dom,
     libxl_dominfo_dispose(&d_info);
 
  endjob:
-    if (!libxlDomainObjEndJob(driver, vm)) {
-        virObjectUnlock(vm);
+    if (!libxlDomainObjEndJob(driver, vm))
         vm = NULL;
-    }
 
  cleanup:
     if (vm)