Fix incorrect onScroll handler on GAL mode.

If a Scroll event is skipped, a default handler is fired by wxWidgets.
This default default handler fires 3 wxEVT_SCROLLWIN_LINEUP or wxEVT_SCROLLWIN_LINEDOWN events.

This is not wanted now in eeschema (and pcbnew) because they add extra (unwanted) scrolling.

Fixes: lp:1810403
https://bugs.launchpad.net/kicad/+bug/1810403

common/view/wx_view_controls.cpp

@@ -213,7 +213,10 @@ void WX_VIEW_CONTROLS::onWheel( wxMouseEvent& aEvent )
         }
     }
 
-    aEvent.Skip();
+    // Do not skip this event, otherwise wxWidgets will fire
+    // 3 wxEVT_SCROLLWIN_LINEUP or wxEVT_SCROLLWIN_LINEDOWN (normal wxWidgets behavior)
+    // and we do not want that.
+    m_parentPanel->Refresh();
 }