Emoji characters in message break the post preview function

[Sesquipedalian]

Original report here

If the message body contains an emoji character (not to be confused with SMF's smileys), trying to get a message preview results in this error message:

The message has the following error or errors that must be corrected before continuing:
The message body was left empty.

Once posted, the message will show up perfectly well in the topic display. It seems that only the preview is affected.