qemu: snapshot: Don't leak XML definition if restarting of CPUs fails

In case the snapshot code isn't able to restart CPUs after an external
checkpoint we would leak a copy of the domains XML definition. This
patch fixes the cleanup path.

src/qemu/qemu_driver.c

@@ -11494,7 +11494,8 @@ endjob:
                            _("resuming after snapshot failed"));
         }
 
-        return -1;
+        ret = -1;
+        goto cleanup;
     }
     if (vm && thaw != 0 &&
         qemuDomainSnapshotFSThaw(driver, vm, thaw > 0) < 0) {