HTTP Server: should include bag in returned tiddlers

The bag field is included in the tiddlers baked into the HTML file, but is also needed on tiddlers read from the server dynamically.

Fixes #4291

core/modules/server/routes/get-tiddler.js

@@ -34,6 +34,7 @@ exports.handler = function(request,response,state) {
 			}
 		});
 		tiddlerFields.revision = state.wiki.getChangeCount(title);
+		tiddlerFields.bag = "default";
 		tiddlerFields.type = tiddlerFields.type || "text/vnd.tiddlywiki";
 		response.writeHead(200, {"Content-Type": "application/json"});
 		response.end(JSON.stringify(tiddlerFields),"utf8");