chatgui: fix invite link and Russian channel name encoding

- chat_sync.c: after invite trampoline, check if connection to invite
  node is already UP and trigger cs_on_conn_up to send CHANNEL_INFO_REQ.
  Fixes invite not completing when connection is reused (Fix 1 side effect).
- mainwindow.cpp: use name.toUtf8().constData() instead of qPrintable()
  to preserve UTF-8 encoding on Windows (Russian channel names).

tools/chatgui/src/mainwindow.cpp

@@ -479,7 +479,7 @@ void MainWindow::onCreateGroupRequested() {
     struct chat_channel_create* req = (struct chat_channel_create*)u_malloc(sizeof(*req));
     memset(req, 0, sizeof(*req));
     snprintf(req->channel_id, sizeof(req->channel_id), "%s", qPrintable(channelId));
-    snprintf(req->name, sizeof(req->name), "%s", qPrintable(name));
+    snprintf(req->name, sizeof(req->name), "%s", name.toUtf8().constData());
     req->owner_node_id = ownerNodeId;
     memcpy(req->x25519_pubkey, x25519_pub, 32);
     memcpy(req->x25519_privkey, x25519_priv, 32);