Fix Klocwork#2051,2060: Array may be outside index

* Added check to ensure _data_len is within index values.

* Had to repeat the branch statement rather than move it because of memcpy.

Signed-off-by: Kevin Moloney <kevin.moloney@emutex.com>

Author: Kevin Moloney

libraries/CurieBle/src/BleCharacteristic.cpp

@@ -165,7 +165,7 @@ BleCharacteristic::_setValue(void)
     if (!_initialised)
         return BLE_STATUS_WRONG_STATE;
 
-    if (_data_len > _char_data.max_len)
+    if (_data_len > BLE_MAX_ATTR_DATA_LEN)
         return BLE_STATUS_NOT_ALLOWED;
 
     status = ble_client_gatts_set_attribute_value(_handles.value_handle,