patch 9.2.0901: textprop: wrong cursor line with truncated virtual text

patch 9.2.0901: textprop: wrong cursor line with truncated virtual text

Problem:  The cursor is displayed in the wrong line when virtual text below
          an empty line is truncated.
Solution: Do not count an extra column for an empty line that has virtual
          text below it, its width already includes filling up the line.
          (Hirohito Higashi).

fixes:  #12493
closes: #20917

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>