fix: clamp cursor on insert escape

[reobin]

• found this while working on a new motion
• avoid leaving cursor on newline after exiting insert
• matches vim behavior so paste lands on the right line

repo steps before this fix:

1. fill input box with abc/nde (\n being a line break)
2. cursor on position 0,0 ("a")
3. do x to remove it
4. do A to go to insert mode at end of line
5. do esc to go back to normal mode
6. do p to paste the "a"
7. it will be pasted on second line, instead of end of first line

[leohenon]

Thanks!