Don't leave wxSubwindows::m_ids uninitialized.

Normally it's initialized by calling Create(), but don't crash deleting an
invalid pointer in the dtor if Create() hadn't been called.

See #16630.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@78046 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/subwin.h

@@ -152,6 +152,7 @@ private:
     {
         m_count = 0;
         m_hwnds = NULL;
+        m_ids = NULL;
     }
 
     // number of elements in m_hwnds array