Fix shortcut dialog toggling

modules/UI/UI.js

  * Shows or hides the keyboard shortcuts panel, depending on the current state.'
  */
 UI.toggleKeyboardShortcutsPanel = function() {
-    let titleKey = 'keyboardShortcuts.keyboardShortcuts';
-    let title = APP.translation.translateString(titleKey);
-    let msg = $('#keyboard-shortcuts').html();
-    let buttons = { Close: true };
+    if (!messageHandler.isDialogOpened()) {
+        let titleKey = 'keyboardShortcuts.keyboardShortcuts';
+        let title = APP.translation.translateString(titleKey);
+        let msg = $('#keyboard-shortcuts').html();
+        let buttons = { Close: true };
+
+        messageHandler.openDialog(title, msg, true, buttons);
+    } else {
+        messageHandler.closeDialog();
+    }
 
-    messageHandler.openDialog(title, msg, true, buttons);
 };
 
 /**

modules/UI/util/MessageHandler.js

 
     enablePopups: function (enable) {
         popupEnabled = enable;
+    },
+
+    /**
+     * Returns true if dialog is opened
+     * false otherwise
+     * @returns {boolean} isOpened
+     */
+    isDialogOpened: function () {
+        return !!$.prompt.getCurrentStateName();
     }
 };