[WiFiScan] Allow allocation to fail and prevent memory leak

When there are many AP's seen during a scan, the allocation of `_scanResult` may fail.
Thus add `(std::nothrow)` to the `new` call.

Also it is possible the array was still present before allocating a new one.

Author: TD-er

libraries/WiFi/src/WiFiScan.cpp

@@ -117,8 +117,13 @@ int16_t
  */
 void WiFiScanClass::_scanDone() {
   esp_wifi_scan_get_ap_num(&(WiFiScanClass::_scanCount));
+  if (WiFiScanClass::_scanResult) {
+    delete[] reinterpret_cast<wifi_ap_record_t *>(WiFiScanClass::_scanResult);
+    WiFiScanClass::_scanResult = 0;
+  }
+
   if (WiFiScanClass::_scanCount) {
-    WiFiScanClass::_scanResult = new wifi_ap_record_t[WiFiScanClass::_scanCount];
+    WiFiScanClass::_scanResult = new (std::nothrow) wifi_ap_record_t[WiFiScanClass::_scanCount];
     if (!WiFiScanClass::_scanResult) {
       WiFiScanClass::_scanCount = 0;
     } else if (esp_wifi_scan_get_ap_records(&(WiFiScanClass::_scanCount), (wifi_ap_record_t *)_scanResult) != ESP_OK) {