... and update a related test case
the original motivation here was garbage _start traces shouldn't be
considered valuable. of course we have way more advanced measurements for
whether a trace is valuable or not. notably the actual rating. so as
long as we have any frame for evaluation that frame's rating is
relevant.
drkonqi is smart enough to ignore lines that do not matter already.
e.g. everything above the crash handler is ignored, equally originator
functions main/start_thread/start/... are ignored. they do not impact
the rating at all, regardless of the amount of frames under review.
as such it is entirely possible to have fewer than 4 frames under review
and that those 4 frames are all we need (e.g. the crash is in main()
directly)
in fact, the very trace sample testing this was proving how the 4 line
limit made no sense. the frame about KCmdLineArgs is the only relevant
and only valuable frame in the sample and it is 100% useful making the
entire trace useful. it is simply a nullptr dereference in the main.
the frame limit is now 1 and the test sample has been replaced with
a real-life sample from https://bugs.kde.org/show_bug.cgi?id=193032