qmlcachegen occasionally generates an invalid cpp file

Our CI system occasionally fails compilation due to an invalid cpp file that was generated by qmlcachegen. By isolating the QML file and rerunning qmlcachegen hundreds of times on that file only, we were able to consistently reproduce the problem. It is possible that the system needs to be under heavier load to increase the occurrence rate.

Scenario:

• Use qmlcachegen to compile Example.qml (See attachment).
• Compile the cpp file that is generated from qmlcachegen.

Expected:
Running qmlcachegen always generates the exact same cpp file that always compiles. (See "OK_Example_qml.cpp" in attachment)

Actual:
Running qmlcachegen has a very slim chance (<1%) of generating an invalid cpp file that does not compile. (See "BAD_Example_qml.cpp" in attachment)