Fails to produce PDF output when using scale.by.width - produces broken...

(I'm just forwarding a bug report from Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=993678)

While building a PDF we stumbled upon an issue. Some of our XML files contain
screen elements with non UTF-8 characters. When we enable scaling for listing
elements:

<xsl:param name="literal.extensions">scale.by.width</xsl:param>

dblatex fails. The produced .tex files then contain line such as:

\begin{lstcode}[escapeinside={<:}{:>}][scale=false,firstnumber=1,escapeinside={<t>}{</t>},moredelim={**[is][\bfseries]{<b>}{</b>}},moredelim={**[is][\itshape]{<i>}{</i>}},]

and those lead to a failure. The problem seems to be code in

/usr/lib/python3/dist-packages/dbtexmf/dblatex/rawverb.py

which fails to detect existing options (added via
/usr/share/xml/docbook/stylesheet/dblatex/xsl/verbatim.xsl already). Thus
dblatex adds another set of options. The same happens without using
scale.by.width, but the resulting lstlisting elements just produce a warning,
that the second set of options gets dropped.

There are several issues I was able to locate. In parse_begin()

if line[0] == b"[":

doesn't seem to work (here they check for existing options). And after fixing
that, the next issue is that

e = line.find(b"]")+1

will fail to produce the desired result because

[scale=false,firstnumber=1,escapeinside={<t>}{</t>},moredelim={**[is][\bfseries]{<b>}{</b>}},moredelim={**[is][\itshape]{<i>}{</i>}},]

contains several closing brackets and we need to find the matching one. Maybe
one could search for ',]'? Not sure if this will break dblatex in other ways.

Next issue then is:

Error: utf_8_encode() argument 2 must be str or None, not bytes

The problem here seems to be in
/usr/lib/python3/dist-packages/dbtexmf/dblatex/rawparse.py and a change in
Python 3 related to string handling.

This problem is a show stopper for us at the moment. Any help is greatly
appreciated.

Attached is a simple testcase. Use it via:

dblatex -d -D -b xetex -p config.xsl test.xml