Proxy: added ctx checking to input filters. The proxy module context may be NULL in case of filter finalization (e.g. by image_filter) followed by an internal redirect. This needs some better handling, but for now just check if ctx is still here.

# Copyright (C) Igor Sysoev
# Copyright (C) Nginx, Inc.


cat << END >> $NGX_AUTO_CONFIG_H

#ifndef $have
#define $have  0
#endif

END