loader/dri3: temporarily work around a crash when front is NULL
Commit c65bde7b introduced a regression where under certain
circumstances front may be NULL, thus leading to a crash. It's not
currently known what exactly causes front to become NULL, nor we can
revert the offending commit, because there had been too many unrelated
changes that now depend on this commit.
There're discussions in #8982 (closed) — basically, not me nor the original author have any idea of what could be causing it. I've spent a lot of time trying to reduce the changes (as I have no knowledge of the functional in question), and also sprinkling various prints in different places, comparing before- and after-, trying gdb record, apitrace (for both of which as result I reported bugs)… To no avail.
At this point, until someone comes up with a proper fix, let's add a workaround to avoid the crash.
- CC: @mareko
- CC: mesa-stable
- Closes: #8982 (closed)