Fix Unicode!

This should fix the mysterious broken-Unicode bug seen in #xkcd.

It turns out that _sometimes_ the channel name (`$chl`) has the utf8 flag set, causing `$text` to be interpreted wrongly (blindly casted to utf8) when they are finally concatenated.

Tested with Perl 5.20. (Requires at least Perl 5.8.1 for `utf8::is_utf8()`.)