Fix CFRelease on null variable when using truncationAttributedText

[MikeDonahue]

I was hitting a crash in ASTextNode2 (in an ASCellNode) while using truncationAttributedText and additionalTruncationMessage. It seemed to only happen on a tap event when maximumNumberOfLines was 0, and the text was long enough to run off screen requiring the user to scroll. The node rendered fine, but crashed as the user touched down to scroll. A quick null check before calling CFRelease was enough to fix it.

[rahul-malik]

@MikeDonahue - Thanks for the fix!