block typing if max length exceeded

[ghost]

When typing a really long message, textsecure used to block the typing when I reached the max length limit. It just happened to me that I exceeded that limit (without noticing) and sent a message that was automatically trimmed while being sent. Please notify the user that the message will be trimmed, or prevent the typing in the first place.
Don't know in which version this problem arose

[ghost]

Just so you know, when I exceeded the 2000-character limit, the number of remaining characters went below the zero
(I'm not working on a fix anymore)

[McLoo]

This can easily be reproduce with pasting rather than typing. Paste 3000, get -1000 left and free typing, until something happens to min integer being -2^31 😁

*why can't I figure out such things on a slot machine or cash dispenser? *

Edit: @mcginty you might want to re-un-jank character count indicators 😉

[agrajaghh]

closing in favor of #5146