Set the int field of wxCommandEvent generated by clicking on the menu items correctly for not checkable items: it is supposed to be -1 and not 0 (which is the value for checkable but currently unchecked items). This was already the case for wxGTK and wxOSX and implied by the comments in the code. Make wxMSW behave like this too and clearly document this behaviour. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69101 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775