Fixed crashes after erasing some strokes and undo.

src/domain/UBGraphicsItemUndoCommand.cpp

@@ -120,8 +120,12 @@ void UBGraphicsItemUndoCommand::undo()
             {
                 UBGraphicsPolygonItem *polygonItem = qgraphicsitem_cast<UBGraphicsPolygonItem*>(item);
                 if (polygonItem)
+                {
+                    mScene->removeItem(polygonItem);
+                    mScene->removeItemFromDeletion(polygonItem);
                     polygonItem->strokesGroup()->addToGroup(polygonItem);
                 }
+            }
 
             UBApplication::boardController->freezeW3CWidget(item, false);
         }
@@ -225,9 +229,13 @@ void UBGraphicsItemUndoCommand::redo()
 
                 UBGraphicsPolygonItem *polygonItem = qgraphicsitem_cast<UBGraphicsPolygonItem*>(item);
                 if (polygonItem)
+                {   
+                    mScene->removeItem(polygonItem);
+                    mScene->removeItemFromDeletion(polygonItem);
                     polygonItem->strokesGroup()->addToGroup(polygonItem);
                 }
             }
+        }
 
         // force refresh, QT is a bit lazy and take a lot of time (nb item ^2) to trigger repaint
         mScene->update(mScene->sceneRect());

src/domain/UBGraphicsScene.cpp

@@ -843,6 +843,7 @@ void UBGraphicsScene::eraseLineTo(const QPointF &pEndPoint, const qreal &pWidth)
 
         //remove full polygon item for replace it by couple of polygons who creates the same stroke without a part which intersects with eraser
         mRemovedItems << intersectedPolygonItem;
+        intersectedPolygonItem->strokesGroup()->removeFromGroup(intersectedPolygonItem);
         removeItem(intersectedPolygonItem);
     }