Don't queue change events for deleting non-existent tiddlers

Fixes #1919

boot/boot.js

@@ -885,10 +885,12 @@ $tw.Wiki = function(options) {
 	this.deleteTiddler = function(title) {
 // Uncomment the following line for detailed logs of all tiddler deletions
 // console.log("Deleting",title,tiddler)
-		delete tiddlers[title];
-		this.clearCache(title);
-		this.clearGlobalCache();
-		this.enqueueTiddlerEvent(title,true);
+		if($tw.utils.hop(tiddler,title)) {
+			delete tiddlers[title];
+			this.clearCache(title);
+			this.clearGlobalCache();
+			this.enqueueTiddlerEvent(title,true);
+		}
 	};
 
 	// Get a tiddler from the store