message: [contour] Sequencer: Ensures invalid XTSMGRAPHIS SetValue for Sixel won't accidentally set image values to 0x0.
diff: @@ -882,6 +882,11 @@ namespace impl // {{{ some command generator helpers
  if (!action.has_value())
  return ApplyResult::Invalid;
  + if (*item != XtSmGraphics::Item::NumberOfColorRegisters
  + && *action == XtSmGraphics::Action::SetToValue
  + && (!Pv || !Pu))
  + return ApplyResult::Invalid;
  +
  auto const value = [&]() -> XtSmGraphics::Value {
  using Action = XtSmGraphics::Action;
  switch (*action) {
  