'Open New' Window positioning

`Open Project` Window pops-up in the middle of the LMMS Window, instead of on the middle of the screen.

This is a gif of my 2-screen set-up: https://streamable.com/lc4pf

It gets quite annoying since the open window is split up between the screens (in same-resolution screens)

Reproduce the Open Project window behavior using the linked two-screen setup, then locate the code that creates and positions this window. Compare its placement with the expected center of the active screen and verify the result on a multi-monitor setup.

Written by the indexing model from the issue text.