Set correct server instance for playlist items

[JonnyWong16]

Description

Sets the correct _server object for playlist items from a different server than the playlist source.

Closes #1461

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have added or updated the docstring for new or existing methods
• [ ] I have added tests when applicable

[JonnyWong16]

@glensc Can you test this PR?

It works but definitely slows down retrieving playlist items if they are from different servers.