Memcached: stricten header validation. An invalid memcached reply that started with '\n' could cause segmentation fault. An invalid memcached reply "VALUE / 0 2\r?ok\r\nEND\r\n" was considered as a valid response. In addition, if memcached reports that the key was not found, set u->headers_in.content_length_n to 0. This ensures that ngx_http_memcached_filter() will not be called while previous code relied on always intercepting 404. Initialization of ctx->rest was moved to where it belongs.