Revert "Merge pull request #847 from code-dot-org/revert_843"

This reverts commit be9e7d7dbf8bfa5ced48db301adc983c698f1030, reversing
changes made to 4fd17377776c2add0c230f3fd84f4d19d88870ae.
Put student register form in else block
Merge pull request #850 from code-dot-org/fix_username_issue

Fix student register form issue