Merge of r5083: fixed potential segfault in keepalive handler. Fixed potential segfault in ngx_http_keepalive_handler(). In case of error in the read event handling we close a connection by calling ngx_http_close_connection(), that also destroys connection pool. Thereafter, an attempt to free a buffer (added in r4892) that was allocated from the pool could cause SIGSEGV and is meaningless as well (the buffer already freed with the pool).