Uninitialized QPageLayout unit makes the whole page size invalid

Default constructor of QPageLayout does not initialize units.
This makes the whole page size invalid - based on random value.

Nothing works if the default ctor is used, even setMargins() fails:

QPageLayout layout;
layout.setMargins(...); // <--

Resolution: attached.

A unit test for the case:
QCOMPARE(QPageLayout().units(), QPageLayout::Point);