screen: commit a wide cell's tail to prev, or the diff leaves a hole

A wide glyph's tail column is never painted or compared, and prev never
learned it either. Overwrite the head later and the terminal blanks the
tail cell -- but if that column's new content matches the stale prev, the
diff skips it, leaving a one-cell hole where the glyph's second half was.

Seen as a missing rule cell in a pane's top border after spawning a new
tab: the old tab's centered title started with a wide glyph, the new
tab's border put the rule back, and the tail column stayed blank.

0 files changed, 0 insertions, 0 deletions