PM: Error when composing a message to user with 1 symbol long username

Preconditions:

1. You should have an activated account on http://qa.jtalks.org/jcommune and be logged in.
2. A user with a username containing only 1 symbol should be registered and activated.

Steps to reproduce:

1. Go to the user's Messages page.
2. Click Compose button.
3. Enter an existed username containing only 1 symbol in the field To.
4. Fill in Subject and Message content fields, click Send button.

AR: Error "User not found" appeares under To field, but the message is sent.
ER: Username is in the field To without any errors. The message is sent.