use current mouse position as default position in wxWindow::PopupMenu (works better in wxGTK and is what you need in majority of cases)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@27599 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/unix/taskbarx11.cpp

@@ -314,6 +314,6 @@ bool wxTaskBarIcon::PopupMenu(wxMenu *menu)
     if (!m_iconWnd)
         return false;
     wxSize size(m_iconWnd->GetClientSize());
-    m_iconWnd->PopupMenu(menu, size.x/2, size.y/2);
+    m_iconWnd->PopupMenu(menu);
     return true;
 }