QWebEngineView::print() does not handle margins properly

When trying to print webpage to PDF using QWebEngineView::print() with all 4 margins specified, the top and left margins work correctly, but webpage is not scaled down properly so that everything is shifted toward bottom right corner. The result is bottom and right margins are abnormally small.

Steps to reproduce the issue:
1. Apply the attached patch to Qt official simple browser example.
2. Run the example.
3. File->Print and print to a PDF.
4. It can be observed that webpage contents are shifted to lower-right corner.

The printer is set up in tabwidget.cpp 'void TabWidget::handlePrintTriggered()'. Printer settings do not help here, e.g., setPagesize, setPageOrientation, etc. do not help solve this margin issue.