gtk: centered album art column displays art right-aligned

[ghost]

Steps to reproduce the problem

1. Create a playlist with Album Art that is much narrower than it is tall
2. Create a center-aligned album art column
3. Art is not centered

What's going on? Describe the problem in as much detail as possible.

Art is right aligned instead of being centered within the column on a high DPI display. Not sure about on a normal DPI display, I do not have one for reference.

Information about the software:

Deadbeef version: 1.9.2 (from arch repositories)
OS: Arch Linux x86_64
Using a high DPI monitor (GTK/Qt scaling factor set to 150%/144dpi)