urwid / urwid / 32698520462

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Text layout: do not crash when a wide character is clipped on both sides (#1241)

LayoutSegment.subseg appended the middle segment without checking its
width. A window that both starts and ends inside one double-width
character leaves nothing between the two padding cells, so that width came
out as zero, and LayoutSegment refuses a segment of zero screen columns.
Rendering CJK or emoji text into a narrow area therefore raised ValueError
instead of drawing, which took down any application whose pane was
narrowed to a few columns.

The halves of the clipped character are already emitted as their own
one-column segments on either side, so the empty one between them carries
nothing and can be left out.

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