multi: pollset assertion only when IP connected

Give warning for an empty pollset only when the connection has at least
IP connectivity. There are cases where the connect in QUIC makes another
attempt on a timeout and no socket will be available during that.

Closes #14108

lib/multi.c

@@ -1198,7 +1198,8 @@ static void multi_getsock(struct Curl_easy *data,
   }
 
   if(expect_sockets && !ps->num &&
-     !(data->req.keepon & (KEEP_RECV_PAUSE|KEEP_SEND_PAUSE))) {
+     !(data->req.keepon & (KEEP_RECV_PAUSE|KEEP_SEND_PAUSE)) &&
+     Curl_conn_is_ip_connected(data, FIRSTSOCKET)) {
     infof(data, "WARNING: no socket in pollset, transfer may stall!");
     DEBUGASSERT(0);
   }