Fix initializing Plex online metadata server multiple times

[JonnyWong16]

Description

Fix initializing Plex online metadata server multiple times when retrieving watchlist or Discover results.

Fixes #1026

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
• [ ] 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