WiFi: fix memory leak on multiple scan()

Author: facchinm

libraries/WiFi/src/WiFi.cpp

@@ -82,7 +82,9 @@ static uint8_t sec2enum(nsapi_security_t sec)
 
 int8_t arduino::WiFiClass::scanNetworks() {
     uint8_t count = 10;
-    ap_list = new WiFiAccessPoint[count];
+    if (ap_list == NULL) {
+        ap_list = new WiFiAccessPoint[count];
+    }
     return wifi_if->scan(ap_list, count);
 }
 

libraries/WiFi/src/WiFi.h

@@ -283,7 +283,7 @@ class WiFiClass
     char* _ssid;
     WiFiInterface* wifi_if;
     voidPrtFuncPtr cb;
-    WiFiAccessPoint* ap_list;
+    WiFiAccessPoint* ap_list = NULL;
     uint8_t connected_ap;
 };