[6.1] Mailing from template fails when signature is on and no plain text

[Jordi Llinares - KM Sistemas]

If you create a mailing template for which you enable user signature and use HTML body instead of plain text, the method 'generate_email' from the 'email_template' module raises an exception (TypeError: unsupported operand type(s) for +=: 'bool' and 'unicode') on line 339

    values['body_text'] += '\n\n' + signature

because this sentence is not encapsulated into a

    if mailbox_values['body_text']:

sentence (contrarily to OpenERP 6.0, where these conditionals were properly programmed).