Events: fixed EPOLLRDHUP with FIONREAD (ticket #2367).

When reading exactly rev->available bytes, rev->available might become 0
after FIONREAD usage introduction in efd71d49bde0.  On the next call of
ngx_readv_chain() on systems with EPOLLRDHUP this resulted in return without
any actions, that is, with rev->ready set, and this in turn resulted in no
timers set in event pipe, leading to socket leaks.

Fix is to reset rev->ready in ngx_readv_chain() when returning due to
rev->available being 0 with EPOLLRDHUP, much like it is already done in
ngx_unix_recv().  This ensures that if rev->available will become 0, on
systems with EPOLLRDHUP support appropriate EPOLLRDHUP-specific handling
will happen on the next ngx_readv_chain() call.

While here, also synced ngx_readv_chain() to match ngx_unix_recv() and
reset rev->ready when returning due to rev->available being 0 with kqueue.
This is mostly cosmetic change, as rev->ready is anyway reset when
rev->available is set to 0.

src/os/unix/ngx_readv_chain.c

@@ -46,6 +46,7 @@ ngx_readv_chain(ngx_connection_t *c, ngx_chain_t *chain, off_t limit)
                 return 0;
 
             } else {
+                rev->ready = 0;
                 return NGX_AGAIN;
             }
         }
@@ -63,6 +64,7 @@ ngx_readv_chain(ngx_connection_t *c, ngx_chain_t *chain, off_t limit)
                        rev->pending_eof, rev->available);
 
         if (rev->available == 0 && !rev->pending_eof) {
+            rev->ready = 0;
             return NGX_AGAIN;
         }
     }