Cache: reset c->body_start when reading a variant on Vary mismatch. Previously, a variant not present in shared memory and stored on disk using a secondary key was read using c->body_start from a variant stored with a main key. This could result in critical errors "cache file .. has too long header".

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


have=NGX_SUPPRESS_WARN . auto/have

have=NGX_SMP . auto/have