Previously r->header_size was used to store length for a part of
value that represents an individual already parsed HTTP header,
while r->header_end pointed to the end of the whole value.

Instead of storing length of a following name or value as pointer
to a potential end address (r->header_name_end and r->header_end)
that might be overflowed, now r->lowercase_index counter is used
to store remaining length of a following unparsed field.

It also fixes incorrect $body_bytes_sent value if a request is
closed while parsing of the request header.  Since r->header_size
is intended for counting header size, thus abusing it for header
parsing purpose was certainly a bad idea.

If something like "error_page 400 @name" is used in a configuration,
a request could be passed to a named location without URI set, and this
in turn might result in segmentation faults or other bad effects
as most of the code assumes URI is set.

With this change nginx will catch such configuration problems in
ngx_http_named_location() and will stop request processing if URI
is not set, returning 500.

If a request is finalized in the first call to the
ngx_http_upstream_process_upgraded() function, e.g., because upstream
server closed the connection for some reason, in the second call
the u->peer.connection pointer will be null, resulting in segmentation
fault.

Fix is to avoid second direct call, and post event instead.  This ensures
that ngx_http_upstream_process_upgraded() won't be called again if
a request is finalized.

The fix removes useless stsc entry in result mp4.
If start_sample == n then current stsc entry should be skipped
and the result stsc should start with the next entry.
The reason for that is start_sample starts from 0, not 1.