_sm_helper_truncate() could be fell into infinite while loop so that page execution time out happend.

Issue Summary

Hi, I would say thanks so much for this great module first.
The minor issue I found is that _sm_helper_truncate() could get into infinite while loop.
I know the page execution time out due to the infinite while loop may be barely happened in real world because there should be a space in the body at least. But I've experienced this infinite loop with my dummy body text which doesn't have any space within first 100 characters.
Cheers.