Fixed error that failed to display user-not-found text in red error box.
Fixed error that failed to display user-not-found text in red error box.

When non-existant people or groups were entered into the review request target
reviewers fields, the error box didn't show the text correctly.

Testing done:
1. Incorrectly inputted into Group field - error appeared with text.
2. Incorrectly inputted into People field - error appeared with text.

Fixes bug 2869.
Reviewed at http://reviews.reviewboard.org/r/3756/

KnowNo/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,chipx86/reviewboard,1tush/reviewboard,bkochendorfer/reviewboard,1tush/reviewboard,1tush/reviewboard,1tush/reviewboard,davidt/reviewboard,bkochendorfer/reviewboard,KnowNo/reviewboard,reviewboard/reviewboard,brennie/reviewboard,sgallagher/reviewboard,davidt/reviewboard,sgallagher/reviewboard,custode/reviewboard,brennie/reviewboard,bkochendorfer/reviewboard,1tush/reviewboard,brennie/reviewboard,beol/reviewboard,davidt/reviewboard,davidt/reviewboard,bkochendorfer/reviewboard,custode/reviewboard,1tush/reviewboard,beol/reviewboard,reviewboard/reviewboard,sgallagher/reviewboard,chipx86/reviewboard,custode/reviewboard,1tush/reviewboard,KnowNo/reviewboard,1tush/reviewboard,custode/reviewboard,1tush/reviewboard,reviewboard/reviewboard,sgallagher/reviewboard,KnowNo/reviewboard,beol/reviewboard,brennie/reviewboard,beol/reviewboard