Avoid setting sash resize cursor when mouse is still over border of second pane with wxGTK

This made it possible to have the resize cursor, but not be able to drag the
sash, and happened because wxGTK sends a leave event when mouse leaves client
area instead of outer border of window. Setting the useless SashHitTest()
"tolerance" parameter to zero avoids the problem.
Fixes #1397


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73110 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/splitter.cpp

@@ -323,7 +323,7 @@ void wxSplitterWindow::OnMouseEvent(wxMouseEvent& event)
     }  // left up && dragging
     else if ((event.Moving() || event.Leaving() || event.Entering()) && (m_dragMode == wxSPLIT_DRAG_NONE))
     {
-        if ( event.Leaving() || !SashHitTest(x, y) )
+        if ( event.Leaving() || !SashHitTest(x, y, 0) )
             OnLeaveSash();
         else
             OnEnterSash();