native_app_glue: fix APP_CMD_TERM_WINDOW pre-hook

The window field must not be set to NULL in the pre-hook, only the
post-one. See http://code.google.com/p/android/issues/detail?id=14352

Change-Id: Ib6214d47c97766bf4a5e148b6b6707e08366fe36
1 file changed