Sometimes, m_x and m_y don't reflect the true position of the window,

Sometimes, m_x and m_y don't reflect the true position of the window,
for example after using wxToolBar::AddControl. This change gets the
actual position if necessary; it fixes a popup window positioning problem
for combo controls on a toolbar.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41176 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775