Some letters don't show when using font other than `systemFont`

[viktoricalonia]

When using other font, some letter's doesn't show.when using ZCLayoutGroupChar, or some words dont show when using ZCLayoutGroupWord.

[viktoricalonia]

fixed on this commit viktoricalonia@b29a9f4.. please check if my approach is wrong.. thank you.

P.S. this is a wonderful library.. :)

[davidtperk]

Unfortunately, this doesn't resolve the problem.