Problem: Unnamed register only contains the last deleted text when
appending deleted text to a register. (Wolfgang Jeltsch)
Solution: Only set y_previous when not using y_append. (Christian Brabandt)
Problem: When several lines are visually selected and one of them is short,
using put may cause a crash. (Axel Bender)
Solution: Check for a short line. (Christian Brabandt)
Problem: When a block is visually selected and put is used on the end of
the selection only one line is changed.
Solution: Check for the end properly. (Christian Brabandt, neovim issue
5781)
Problem: When a multi-byte character ends in a zero byte, putting blockwise
text puts it before the character instead of after it.
Solution: Use int instead of char for the character under the cursor.
(Luchr, closes#1403) Add a test.
