patch 9.2.0850: MS-Windows: commands from a client can be lost

patch 9.2.0850: MS-Windows: commands from a client can be lost

Problem:  On MS-Windows commands sent by a client in quick succession,
          e.g. repeated "--remote-tab", can be lost: the files are not
          all opened (eight)
Solution: In the GUI the client message is handled re-entrantly, e.g.
          while a command line is being read during a redraw. Inserting
          the received keys into the typeahead buffer then corrupts it.
          Postpone inserting the keys until a safe point where the
          typeahead buffer is empty (Hirohito Higashi).

fixes:  #20810
closes: #20816

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>