[bug] Style PositionPlacement Center confused in multi monitor setup

Hi,

I have opened an issue about PositionPlacement Center style: after the rece=
nt changes,
in multi monitor mode, this centers window split between left and right mon=
itor, while with
latest fvwm3 release, this was not the case. Using dv/pager-noaspect where =
the current
issues have been resolved couple days ago. It is repeatable on the current =
master.

Here it is. together with the screenshot of the area between monitors.
https://github.com/fvwmorg/fvwm3/issues/648