fillRect + Anti-Aliasing + hi-dpi Scaling => missing filled pixels

fillRect misses to fill one pixel high lines at start or end of area if the scaling is fractional.

This even happens if you e.g. just fill simple x * 14 pixel regions, you will often have 1 pixel empty lines in-between such groups.

see https://bugreports.qt.io/browse/QTBUG-66036?focusedCommentId=479175&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-479175

Turning off anti-aliasing rectifies this issue.

This leads to strange rendering artifacts in many applications, like linked above in KWrite.
There I worked around this by turning AA off before I call fillRect, thought this is not expected.
(and seems only to happen in combination with some QT_SCALE_FACTOR or otherwise triggered fractional hi-dpi scaling)