Steps to reproduce the issue

1. Make sure you have one or more distinctive words entered in the Banned Subject and Banned Text fields of a contact.
2. On the front-end, go to the form for the contact and try to send a message with the subject and/or message containing one of the banned words.

Expected result

An error message should be shown to say that a field was in error. No contact email should be sent.

Actual result

No error message is shown and the contact email is sent.

System information (as much as possible)

Joomla 2.5.24

Additional comments

Fix is trivial. I'll submit a PR shortly.