Don't remove keybinding if it wasn't added

src/modules/TimerOndemand.js

@@ -41,6 +41,7 @@ var TimerOndemand = class {
 
     constructor() {
         this._button = null;
+        this._previousKeybinding = null;
         this._ondemandKeybindingConnect = null;
         this._ondemandButtonPlacementConnect = null;
     }
@@ -99,6 +100,7 @@ var TimerOndemand = class {
 
 
     _addKeybinding() {
+        this._previousKeybinding = e.settingsManager.ondemandKeybinding;
         if (!e.settingsManager.ondemandKeybinding)
             return;
         logDebug('Adding On-demand Timer keybinding...');
@@ -113,10 +115,12 @@ var TimerOndemand = class {
     }
 
     _removeKeybinding() {
+        if (this._previousKeybinding) {
             logDebug('Removing On-demand Timer keybinding...');
             main.wm.removeKeybinding('nightthemeswitcher-ondemand-keybinding');
             logDebug('Removed On-demand Timer keybinding.');
         }
+    }
 
     _addButton() {
         switch (e.settingsManager.ondemandButtonPlacement) {