When a version tag is deleted, delete it's workflow instance, if it exists. Fixes bug #11544.

docs/changelog/7.x.x.txt

@@ -3,6 +3,7 @@
  - fixed #11557: Shop credit deduction calculated incorrectly
  - fixed #11561: PayDriver_Cash - password help
  - fixed #11541: running workflows screen
+ - fixed #11544: VersionTag Workflows with missing Version Tags run forever
 
 7.9.4
  - We're shipping underscore.js now for its suite of extremely handy utility

lib/WebGUI/VersionTag.pm

@@ -640,6 +640,10 @@ sub rollback {
         $outputSub->(sprintf $i18n->get('Rolling back %s'), $revision->getTitle);
 		$revision->purgeRevision;
 	}
+    my $instance = $self->getWorkflowInstance;
+    if ($instance) {
+        $instance->delete;
+    }
 	$session->db->write("delete from assetVersionTag where tagId=?", [$tagId]);
 	$self->clearWorking;
 	return 1;