Mp4: fix seeks to standalone last chunk. If seek position is within the last track chunk and that chunk is standalone (stsc entry describes only this chunk) such seek generates stsc seek error. The problem is that chunk numbers start with 1, not with 0.

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


have=NGX_SUPPRESS_WARN . auto/have

have=NGX_SMP . auto/have