chatgui: fix corrupted channel_id from non-null-terminated binary protocol

QString::fromUtf8(ch_id) read past length-prefixed string, capturing garbage.
Use fromUtf8(ch_id, ch_id_len) — length already available from bridge but was unused.
Messages now appear on refresh and unread badge correctly matches channel.

tools/chatgui/src/mainwindow.cpp

@@ -32,9 +32,8 @@ extern "C" {
 static MainWindow* s_mainWindow = nullptr;
 
 static void onMsgReceivedCallback(const char* ch_id, int ch_id_len, uint64_t author) {
-    Q_UNUSED(ch_id_len);
     if (s_mainWindow)
-        s_mainWindow->onMessageReceived(ch_id, author);
+        s_mainWindow->onMessageReceived(ch_id, ch_id_len, author);
 }
 
 static void onChannelUpdatedCallback(const char* ch_id, int ch_id_len) {
@@ -334,8 +333,8 @@ void MainWindow::showSettings() {
     dlg.exec();
 }
 
-void MainWindow::onMessageReceived(const char* ch_id, uint64_t author) {
-    QString cid = QString::fromUtf8(ch_id);
+void MainWindow::onMessageReceived(const char* ch_id, int ch_id_len, uint64_t author) {
+    QString cid = QString::fromUtf8(ch_id, ch_id_len);
     DEBUG_INFO(DEBUG_CATEGORY_DEBUG, "MainWindow::onMessageReceived ch=%s author=%llu cur=%s",
                qPrintable(cid), (unsigned long long)author, qPrintable(m_currentChannelId));
     if (m_db && author != m_db->myNodeId())

tools/chatgui/src/mainwindow.h

@@ -31,7 +31,7 @@ private slots:
     void showSettings();
 
 public:
-    void onMessageReceived(const char* ch_id, uint64_t author);
+    void onMessageReceived(const char* ch_id, int ch_id_len, uint64_t author);
     void onMembersChanged(const char* ch_id);
     void onAutoConnectStatus(uint8_t status, uint16_t total, uint16_t totalNodes, uint16_t connected);
     void onChannelPeersOnline(const char* ch_id, int ch_id_len, uint16_t online);