return "ERR: scan already running" on scan command when another scan is still running

src/ebusd/bushandler.cpp

@@ -929,6 +929,9 @@ void BusHandler::receiveCompleted() {
 }
 
 result_t BusHandler::startScan(bool full) {
+  if (m_runningScans > 0) {
+    return RESULT_ERR_DUPLICATE;
+  }
   deque<Message*> messages = m_messages->findAll("scan", "", true);
   for (deque<Message*>::iterator it = messages.begin(); it < messages.end(); it++) {
     Message* message = *it;

src/ebusd/mainloop.cpp

@@ -1157,6 +1157,9 @@ string MainLoop::executeGrab(vector<string> &args) {
 string MainLoop::executeScan(vector<string> &args) {
   if (args.size() == 1) {
     result_t result = m_busHandler->startScan();
+    if (result == RESULT_ERR_DUPLICATE) {
+      return "ERR: scan already running";
+    }
     if (result != RESULT_OK) {
       logError(lf_main, "scan: %s", getResultCode(result));
     }