refactor: simpler rejoin

remove pointless app.cacheBuster = null

public/src/app.js

@@ -7,7 +7,6 @@ app.isFocused = true;
 app.currentRoom = null;
 app.widgets = {};
 app.flags = {};
-app.cacheBuster = null;
 
 (function () {
 	let appLoaded = false;

public/src/sockets.js

@@ -172,37 +172,11 @@ socket = window.socket;
 	}
 
 	function reJoinCurrentRoom() {
-		const	url_parts = window.location.pathname.slice(config.relative_path.length).split('/').slice(1);
-		let room;
-
-		switch (url_parts[0]) {
-			case 'user':
-				room = 'user/' + (ajaxify.data ? ajaxify.data.theirid : 0);
-				break;
-			case 'topic':
-				room = 'topic_' + url_parts[1];
-				break;
-			case 'category':
-				room = 'category_' + url_parts[1];
-				break;
-			case 'recent':
-				room = 'recent_topics';
-				break;
-			case 'unread':
-				room = 'unread_topics';
-				break;
-			case 'popular':
-				room = 'popular_topics';
-				break;
-			case 'admin':
-				room = 'admin';
-				break;
-			case 'categories':
-				room = 'categories';
-				break;
-		}
+		if (app.currentRoom) {
+			const current = app.currentRoom;
 			app.currentRoom = '';
-		app.enterRoom(room);
+			app.enterRoom(current);
+		}
 	}
 
 	function onReconnecting() {