small change increasing the stability of the undo/redo framework

forms/mainwindow.ui

@@ -578,9 +578,6 @@
    <property name="toolTip">
     <string>Save CognitiveMap</string>
    </property>
-   <property name="shortcut">
-    <string>Ctrl+S</string>
-   </property>
    <property name="visible">
     <bool>false</bool>
    </property>

src/GraphicView.cpp

@@ -1169,6 +1169,8 @@ void jpsGraphicsView::Undo()
 {
     if (!_undoStack.IsEmpty())
     {
+        emit no_drawing();
+
         const LineAction recentAction = _undoStack.GetRecentAction();
 
         if (recentAction.GetName()=="LineDeleted")
@@ -1196,6 +1198,8 @@ void jpsGraphicsView::Redo()
 {
     if (!_redoStack.IsEmpty())
     {
+        emit no_drawing();
+
         const LineAction recentAction = _redoStack.GetRecentAction();
 
         if (recentAction.GetName()=="LineDeleted")