subproblem swallows title attribute

[kohlhase]

In MathHub/problems/maai-test/source/theoinf/prob/place-value-systems.en.tex we have

  \begin{subproblem}[title={6-Bit, positive}]
    How to binary code the given decimal number?

and the title does not have any effect. I think insted of

  }\item[\int_use:N \g__problems_subproblem_int .]

in line 237 of problem.sty we should have something like

  }\item[\int_use:N \g__problems_subproblem_int (\g__problems_subproblem_title) .]

but with the correct conditional to make the ( and ) only when there is a title.