Prevent iOS7 (in a contained view) from thinking that it should auto-resize
the stretchable text view when there’s actually no text to stretch up.

Appears to still resize down as the first check is against !isShrinking.
Merge branch 'master' of https://github.com/jessesquires/MessagesTableViewController into issue_61_fix
Merge branch 'master' of https://github.com/jessesquires/MessagesTableViewController into issue_61_fix
Merge pull request #62 from scottcc/issue_61_fix

Prevent iOS7 (in a contained view) thinking that it should auto-resize with empty text.