We shouldn't write a typeinfo entry to qmldir if there is not qmltypes file

Question: Should typeinfo plugins.qmltypes be written to the qmldir file if there's no plugins.qmltypes file installed? Currently we always write it

This should be fixed, if there's no .qmltypes, don't write that entry into qmldir.

Quickly scanning through the code, i think it's always written at the moment.

Resulted from CMake API review: https://git.qt.io/alcroito/qt6-cmake-api-review/-/blob/master/api_review_qt_6_2.md