nghttpx: Revert part of 6f58434d89

The reverted part of the change may use not connected socket in HTTP/1
backend.

src/shrpx_client_handler.cc

@@ -81,11 +81,13 @@ void readcb(struct ev_loop *loop, ev_io *w, int revents) {
     delete handler;
     return;
   }
+  if (ev_is_active(handler->get_wev())) {
     if (handler->do_write() != 0) {
       delete handler;
       return;
     }
   }
+}
 } // namespace
 
 namespace {