Mp4: fixed potential overflow in ngx_http_mp4_crop_stts_data(). Both "count" and "duration" variables are 32-bit, so their product might potentially overflow. It is used to reduce 64-bit start_time variable, and with very large start_time this can result in incorrect seeking. Found by Coverity (CID 1499904).

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


have=NGX_SUPPRESS_WARN . auto/have

have=NGX_SMP . auto/have