assert in QString.h when loading a QML-File using static Qt on Windows

I'm building a qml-application using a self-compiled static Qt 5.12.

When starting the application, I get  an assert:

 ASSERT: "uint(i) < uint(size())" in file /space/qt/qt-everywhere-src-5.12.4/qtbase/include/QtCore/../../src/corelib/tools/qstring.h, line 938
 

This is because in the method QQml_isFileCaseCorrect in qqmlengine.cpp, the check for ':' as the first character (line 2532) doesn't check if the string is empty.
So just replacing

     if (absolute[0] == QLatin1Char(':'))

with

     if (absolute.isEmpty() || absolute[0] == QLatin1Char(':'))

will fix this.

Unfortunately I couldn't reproduce the assert with a simple example program.