add method to check if key sequence is none

src/Gui/Widgets.cpp

@@ -365,10 +365,17 @@ void ActionSelector::on_downButton_clicked()
 AccelLineEdit::AccelLineEdit ( QWidget * parent )
   : QLineEdit(parent)
 {
-    setText(tr("none"));
+    noneStr = tr("none");
+    setText(noneStr);
     keyPressedCount = 0;
 }
 
+bool AccelLineEdit::isNone() const
+{
+    QString t = text();
+    return t.isEmpty() || t == noneStr;
+}
+
 /**
  * Checks which keys are pressed and show it as text.
  */
@@ -386,7 +393,7 @@ void AccelLineEdit::keyPressEvent ( QKeyEvent * e)
     case Qt::Key_Backspace:
         if (state == Qt::NoModifier) {
             keyPressedCount = 0;
-            setText(tr("none"));
+            setText(noneStr);
         }
     case Qt::Key_Control:
     case Qt::Key_Shift:

src/Gui/Widgets.h

@@ -124,13 +124,15 @@ class GuiExport AccelLineEdit : public QLineEdit
   Q_OBJECT
 
 public:
-  AccelLineEdit ( QWidget * parent=0 );
+    AccelLineEdit(QWidget * parent=0);
+    bool isNone() const;
 
 protected:
-  void keyPressEvent ( QKeyEvent * e);
+    void keyPressEvent(QKeyEvent * e);
 
 private:
-  int keyPressedCount;
+    QString noneStr;
+    int keyPressedCount;
 };
 
 // ------------------------------------------------------------------------------