x11/xterm: update to 348

Patch #384 - 2023/07/10
- exclude ASCII space from showMissingGlyphs, since a few bitmap fonts lack
  this (report by "SanRemo", Emanuel Haupt).
- correct a step in rendering double-width characters with bitmap-fonts
  (report by Peter Fabinski, Debian #1039986).
- fixes for ReGIS-related problems (report by Ben Wong):
    - mimic an undocumented hardware VT340 feature which handles color
      initialization with incomplete parameters.
    - handle whitespace between operator/operands for color values.
    - reset ReGIS-context when resetting graphics in RIS.

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