Avoid crashes due to insanely large columns in tabulated-list-format
* src/xdisp.c (append_stretch_glyph, produce_xwidget_glyph)
(produce_image_glyph): Limit the pixel width of the produced glyph
to SHRT_MAX. (Bug#23178)
(append_composite_glyph, append_glyph, append_glyphless_glyph):
Add assertions to verify that the pixel width of the glyph will
never overflow a 'short'.
* src/term.c (append_composite_glyph): Add assertion to verify
that the pixel width of the glyph will never overflow a 'short'.