Fix TextEdit's character limit

[Serverator]

Objective

Fixes a issue with TextEdit's character limit. Currently, the character limit is using bytes instead of chars to count the existing length of the text, which causes incorrect behavior with non-ASCII text. This small PR fixes the issue.

Issue example

If I set a character limit to 8, TextEdit will not allow me to write anything after

• "Language" (8 bytes, 8 chars)
• "Морж" (8 bytes, 4 chars)
• "冰淇淋" (9 bytes, 3 chars)

While still not being at the character limit.

[Wumpf]

makes sense! Wondering if there's more of these hidden