focus-new-window@mdpenguin: Fix disconnection try on possibly null signal id values (#649)

Author: anaximeno

focus-new-window@mdpenguin/files/focus-new-window@mdpenguin/extension.js

@@ -17,8 +17,16 @@ class SettingsHandler {
 
 class AttentionHandler {
   init() {
-    global.display.disconnect(Main.windowAttentionHandler._windowDemandsAttentionId);
-    global.display.disconnect(Main.windowAttentionHandler._windowMarkedUrgentId);
+    if (Main.windowAttentionHandler._windowDemandsAttentionId) {
+      global.display.disconnect(Main.windowAttentionHandler._windowDemandsAttentionId);
+      Main.windowAttentionHandler._windowDemandsAttentionId = null;
+    }
+
+    if (Main.windowAttentionHandler._windowMarkedUrgentId) {
+      global.display.disconnect(Main.windowAttentionHandler._windowMarkedUrgentId);
+      Main.windowAttentionHandler._windowMarkedUrgentId = null;
+    }
+
     oldHandler = Main.windowAttentionHandler;
 
     this._windowDemandsAttentionId = global.display.connect('window-demands-attention', this._onWindowDemandsAttention.bind(this));