fix: harden CLI and GPS handling

examples/simple_sensor/main.cpp

@@ -165,6 +165,7 @@ void loop() {
   if (len > 0 && command[len - 1] == '\r') {  // received complete line
     command[len - 1] = 0;  // replace newline with C string null terminator
     char reply[160];
+    reply[0] = 0;
     the_mesh.handleCommand(0, command, reply);  // NOTE: there is no sender_timestamp via serial!
     if (reply[0]) {
       Serial.print("  -> "); Serial.println(reply);