Don't skip handled mouse wheel events in wxVScrolledWindow.

Make the code consistent with wxScrolledWindow and fix the problem with wheel
events always being skipped by wxVScrolledWindow which could result in
processing them multiple times, e.g. for the window itself and its parent as
it happened with wxPGChoiceEditor cells in wxPropertyGrid.

Closes #15547.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74939 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/vscroll.cpp

@@ -142,6 +142,7 @@ bool wxVarScrollHelperEvtHandler::ProcessEvent(wxEvent& event)
     else if ( evType == wxEVT_MOUSEWHEEL )
     {
         m_scrollHelper->HandleOnMouseWheel((wxMouseEvent &)event);
+        return true;
     }
 #endif
 #endif // wxUSE_MOUSEWHEEL