[FIX] base_vat: Improved the warning message poped up when online VIES v...

...dation fails. (Maintenance Case: 609823)

When the system set to check the vat number entered in customer's form view online(by checking the "VIES VAT Check" field in company form view) and if it failed as it was not a valid number, the system will still show the warning message,
"This VAT number does not seem to be valid.
Note: the expected format is CHE-123.456.788 TVA or CH TVA 123456"

The system should suggest that the VIES VAT validation was failed.

This branch will do so, kindly review it.

Thanks.