The tree can change shape during handling the mousePressEvent() event,
because some part of the tree can be (un)folded. This might lead to
shift of the three (up or down). The position of items in tree change
relatively to the position of mouse (which stays in place).
If the visibility click is handled after mousePressEvent, the shift in
position can lead to cursor beeing over visibility icon and the click
is handled like if the visibility icon vas clicked, which is unexpected.
Handling the visibility click first fixes this. The setAccepted(true),
was removed, it is left to the subroutine to set it.
a9d3a8eb6c