EncryptedBatteryMonitor: fix memory management bugs

There was a buffer overflow in the EncryptedBatteryMonitor example code
when formatting the 6-digit confirmation code for display during
pairing, since the terminating null character was not accounted for in
the buffer size.

Also, there was a memory leak due to unnecessary dynamic allocation
when setting the initial value of the string characteristic.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

Author: pillo79

examples/Peripheral/EncryptedBatteryMonitor/EncryptedBatteryMonitor.ino

@@ -59,7 +59,7 @@ void setup() {
   BLE.setDisplayCode([](uint32_t confirmCode){
     Serial.println("New device pairing request.");
     Serial.print("Confirm code matches pairing device: ");
-    char code[6];
+    char code[7];
     sprintf(code, "%06d", confirmCode);
     Serial.println(code);
   });
@@ -176,8 +176,7 @@ void setup() {
 
     BLE.addService(batteryService);               // Add the battery service
     batteryLevelChar.writeValue(oldBatteryLevel); // set initial value for this characteristic
-    char* stringCharValue = new char[32];
-    stringCharValue = "string";
+    const char* stringCharValue = "string";
     stringcharacteristic.writeValue(stringCharValue);
     secretValue.writeValue(0);