Use wxGetInstance() instead of wxhInstance in wxMSW code.

No real changes, just use an accessor function instead of directly accessing
the global variable.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63554 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/msgdlg.cpp

@@ -267,7 +267,7 @@ void wxMessageDialog::ReplaceStaticWithEdit()
                         rc.right - rc.left, rc.bottom - rc.top,
                         GetHwnd(),
                         NULL,
-                        wxhInstance,
+                        wxGetInstance(),
                         NULL
                       );