Use _UNICODE instead of UNICODE in wx/msw/winundef.h.

This is consistent with the other checks and generally more correct.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63658 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/winundef.h

@@ -123,11 +123,11 @@
 
     inline HWND APIENTRY FindText(LPFINDREPLACE lpfindreplace)
     {
-        #ifdef UNICODE
+        #ifdef _UNICODE
             return FindTextW(lpfindreplace);
         #else
             return FindTextA(lpfindreplace);
-        #endif // !UNICODE
+        #endif
     }
 #endif