[3.4.x] media library: perform UIKit call on main thread

This ensure those 2 calls to be run on the main thread instead of a background thread.

(cherry picked from commit f9ccd4b8, backport of !1010 (merged))

changed milestone to %3.4.2

added 5 commits

• 68966db9...53d32f0f - 4 commits from branch videolan:3.4.x
• a61d4b6b - media library: perform UIKit call on main thread

Compare with previous version

enabled an automatic merge when the pipeline for a61d4b6b succeeds

merged