[inputfilter] SILE's output is non-deterministic (in at least one more case)

[ctrlcctrlv]

#972 and #532 have not been fully solved.

MWE on SILE v0.10.9.r36-gf16af44:

\begin[class=book]{document}
\script[src=packages/frametricks]
\script[src=packages/rebox]
\begin{script}
  local inputfilter = require("packages/inputfilter").exports
  local noop = function (input, _) return input end
  SILE.registerCommand("nondet", function(_, content)
    SILE.process(inputfilter.transformContent(content, noop))
  end)
\end{script}
\nondet{
\font[family=EB Garamond,size=12pt]
\define[command=SILE]{S\lower[height=0.5ex]{I}L\glue[width=-.2em]\raise[height=0.6ex]{\font[size=0.8em]{E}}}
\typeset-into[frame=folio]{\begin[size=12pt]{font}\hfill This document was typeset with \SILE.\end{font}}
}
\end{document}

Without inputfilter noop:

With:

[alerque]

Confirmed. Simplified MWE:

\begin{document}
\begin{script}
  local inputfilter = require("packages/inputfilter").exports
  local noop = function (input, _) return input end
  SILE.registerCommand("nondet", function(_, content)
    SILE.process(inputfilter.transformContent(content, noop))
  end)
\end{script}
\define[command=bar]{S}
\nondet{\hfill \bar.}
\end{document}

Running this on a loop shows the output order flipping back and forth:

$ watch -n1 -d sile -b debug nondet.sil -o /dev/stdout