Copy filter: fixed sendfile aio handlers to set ctx->aio. Sendfile handlers (aio preload and thread handler) are called within ctx->output_filter() in ngx_output_chain(), and hence ctx->aio cannot be set directly in ngx_output_chain(). Meanwhile, it must be set to make sure loop within ngx_output_chain() will be properly terminated. There are no known cases that trigger the problem, though in theory something like aio + sub filter (something that needs body in memory, and can also free some memory buffers) + sendfile can result in "task already active" and "second aio post" alerts. The fix is to set ctx->aio in ngx_http_copy_aio_sendfile_preload() and ngx_http_copy_thread_handler(). For consistency, ctx->aio is no longer set explicitly in ngx_output_chain_copy_buf(), as it's now done in ngx_http_copy_thread_handler().