Split Lines and Column Wrap corruption on long line

Fill a file with `aaa` + space, 60-80k+ size in total. Ctrl+A, Ctrl+I - notice how the first line lost one or two `a`s. Same issue with Ctrl+Shift+W. I have tested with improved #320 but do test with the original implementation, it might be bogus as well.

Same problem with Cyrillic symbols: `ффф` + space, several `ф`s lost.