Log Message:
x11/xterm: update to 375

 - improve error-recovery when setting a bitmap font for the VT100 window, e.g.,
   in case OSC 50 failed, restoring the most recent valid font so that a
   subsequent OSC 50 reports this correctly (report by David Leadbeater).
 - exclude MC_XDG_OPEN from environment variables trimmed on startup (report by
   Gabor Hauzer).
 - check for null pointer in isSelect() (report by Column Paget).