patch 9.2.0569: out-of-bounds access in libvterm CSI 8 t resize

patch 9.2.0569: out-of-bounds access in libvterm CSI 8 t resize

Problem:  In the bundled libvterm the CSI 8 ; rows ; cols t sequence reaches
          on_resize() without validating its arguments.  Missing, zero or
          negative dimensions cause a negative-size memmove() in
          resize_buffer() and out-of-bounds accesses in set_lineinfo() and
          DECALN, all reachable from output rendered in a terminal window
          (Yukihiro Nakamura).
Solution: Reject missing, zero or negative dimensions before calling
          on_resize().  Also clamp a negative cell width in on_text() as
          hardening for the bundled libvterm.

Signed-off-by: Christian Brabandt <cb@256bit.org>