fix ble send message buffer handling

examples/companion_radio/MyMesh.cpp

@@ -1183,6 +1183,8 @@ void MyMesh::handleCmdFrame(size_t len) {
     memcpy(&msg_timestamp, &cmd_frame[i], 4);
     i += 4;
     const char *text = (char *)&cmd_frame[i];
+    int text_len = len - i;
+    cmd_frame[len] = '\0';  // Null-terminate for C string use
 
     if (txt_type != TXT_TYPE_PLAIN) {
       writeErrFrame(ERR_CODE_UNSUPPORTED_CMD);