ThemeSettingsWidget crashes when list of themes empty

I built the git version and according to https://wiki.qt.io/index.php?title=Building_Qt_Creator_from_Git&oldid=19441 started without installing.

Apparently that doesn't work properly due to themes not being found. First a proper warning is shown:

Warning: no themes found in path: "/home/zulan/code/BUILD-qt-creator/DEBUG/share/qtcreator/themes"

But then qt-creator crahes:

ASSERT failure in QList<T>::operator[]: "index out of range", file /usr/include/qt/QtCore/qlist.h, line 518

Program received signal SIGABRT, Aborted.
0x00007ffff478f5f8 in raise () from /usr/lib/libc.so.6
(gdb) bt
#0 0x00007ffff478f5f8 in raise () from /usr/lib/libc.so.6
#1 0x00007ffff4790a7a in abort () from /usr/lib/libc.so.6
#2 0x00007ffff598afc1 in QMessageLogger::fatal(char const*, ...) const () from /usr/lib/libQt5Core.so.5
#3 0x00007ffff5986191 in qt_assert_x(char const*, char const*, char const*, int) () from /usr/lib/libQt5Core.so.5
#4 0x00007fffe36bc293 in QList<Core::Internal::ThemeEntry>::operator[] (this=0x7fffffffc070, i=0) at /usr/include/qt/QtCore/qlist.h:518
#5 0x00007fffe36b8cfe in Core::Internal::ThemeSettingsWidget::refreshThemeList (this=0x96c460)
at /home/zulan/code/qt-creator/src/plugins/coreplugin/themesettingswidget.cpp:252
#6 0x00007fffe36b8504 in Core::Internal::ThemeSettingsWidget::ThemeSettingsWidget (this=0x96c460, parent=0x96c600)
at /home/zulan/code/qt-creator/src/plugins/coreplugin/themesettingswidget.cpp:209

The reason is rather obvious, the code tries to index an empty list of themes.