nghttpx: Revert part of 6f58434d

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

src/shrpx_client_handler.cc

@@ -81,9 +81,11 @@ void readcb(struct ev_loop *loop, ev_io *w, int revents) {
     delete handler;
     return;
   }
-  if (handler->do_write() != 0) {
-    delete handler;
-    return;
+  if (ev_is_active(handler->get_wev())) {
+    if (handler->do_write() != 0) {
+      delete handler;
+      return;
+    }
   }
 }
 } // namespace