Event pipe: fixes for complex protocols. 1. In ngx_event_pipe_write_chain_to_temp_file() make sure to fully write all shadow buffers up to last_shadow. With this change recycled buffers cannot appear in p->out anymore. This also fixes segmentation faults observed due to ngx_event_pipe_write_chain_to_temp() not freeing any raw buffers while still returning NGX_OK. 2. In ngx_event_pipe_write_to_downstream() we now properly check for busy size as a size of buffers, not a size of data in these buffers. This fixes situations where all available buffers became busy (including segmentation faults due to this). 3. The ngx_event_pipe_free_shadow_raw_buf() function is dropped. It's incorrect and not needed.