Improved logging of invalid headers. In 71edd9192f24 logging of invalid headers which were rejected with the NGX_HTTP_PARSE_INVALID_HEADER error was restricted to just the "client sent invalid header line" message, without any attempts to log the header itself. This patch returns logging of the header up to the invalid character and the character itself. The r->header_end pointer is now properly set in all cases to make logging possible. The same logging is also introduced when parsing headers from upstream servers.