Crashes after update due to qmlcache

This is a restatement of the issue described in https://musescore.org/en/node/308981 and https://bugreports.qt.io/browse/QTBUG-85967 .

It happens on Linux (NixOS) with Qt 5.12.7 and Qt 5.12.9. It does not happen with the official AppImage builds with Qt 5.9.8.

MuseScore 3.5.0 crashes on qmlcache generated by running MuseScore 3.4.2. To reproduce with the released versions:
1. Delete ~/.cache/MuseScore/MuseScore3/qmlcache (just in case).
2. Run MuseScore 3.4.2 (complete the configuration wizard if you have not completed it yet) and exit it.
3. Run MuseScore 3.5.0.
It crashes when the splash screen says "Initializing main window" with the attached backtrace bt-3.5.0.txt.

To reproduce with unreleased builds:
1. Delete ~/.cache/MuseScore/MuseScore3Development/qmlcache
2. Run MuseScore 7569ebb7b4d467c2c45f4d84ad966ba25b4351de (or 2ed4a7e86ce8c91c851c756c242ce6fbb06329c8 but not later) and exit it.
3. Run MuseScore 58b14547bb5997688fb6c0dd8d04697b7fae21a1 (but not earlier).
It crashes in the same way. Note that MuseScore built between the mentioned commits neither crashes on the qmlcache created on step 2, nor generates qmlcache that would crash step 3.