remote: avoid memory leak

Leak present since introduction of remoteDomainBuildEventGraphics
in commit 987e31ed.

* src/remote/remote_driver.c: fix memory leak.
Signed-off-by: NAlex Jia <ajia@redhat.com>

src/remote/remote_driver.c

@@ -3294,6 +3294,7 @@ no_memory:
         VIR_FREE(subject->identities);
         VIR_FREE(subject);
     }
+    virDomainFree(dom);
     return;
 }