clear mdns.queryservice()'s previous result when called (#4894)

cleared the linkedlist.
* issue #4893

Author: a-c-sreedhar-reddy

libraries/ESP8266mDNS/ESP8266mDNS.cpp

@@ -289,7 +289,13 @@ int MDNSResponder::queryService(char *service, char *proto) {
 #ifdef DEBUG_ESP_MDNS_TX
   DEBUG_ESP_PORT.printf("queryService %s %s\n", service, proto);
 #endif  
-  
+  while(_answers!=0){
+    MDNSAnswer *currAnswer = _answers;
+    _answers = _answers->next;
+    os_free(currAnswer->hostname);
+    os_free(currAnswer);
+    currAnswer = 0;
+  }
   if (_query != 0) {
     os_free(_query);
     _query = 0;