fdo#45962: fix context menu key yanking cursor out of header/footer

For the "context menu" key VCL synthesizes a cursor position that is the
center of the window, hence likely to be in the document body.
When SwEditWin::Command calls lcl_CheckHeaderFooterClick, it then moves
the document view cursor; prevent that by only calling that for actual
mouse events.  (regression from a6176612)

sw/source/ui/docvw/edtwin.cxx

@@ -4733,7 +4733,7 @@ void SwEditWin::Command( const CommandEvent& rCEvt )
             if (rView.GetPostItMgr()->IsHit(rCEvt.GetMousePosPixel()))
                 return;
 
-            if ( lcl_CheckHeaderFooterClick( rSh,
+            if (rCEvt.IsMouseEvent() && lcl_CheckHeaderFooterClick( rSh,
                         PixelToLogic( rCEvt.GetMousePosPixel() ), 1 ) )
                 return;