Problem: getregionpos() wrong with blockwise mode and multibyte.
Solution: Use textcol and textlen instead of start_vcol and end_vcol.
Handle coladd properly (zeertzjq).
Also remove unnecessary buflist_findnr() in add_regionpos_range(), as
getregionpos() has already switched buffer.
closes: #14805
Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
c95e64f41f
