Add a Malay translation.

The composition of the translation team can be found on Transifex: https://www.transifex.com/projects/p/mpc-hc/language/ms_MY/members/.
Fix: Update the chapter marks on the seekbar when the media length changes.

Mostly useful for MKV with multiple editions.

Fixes #3963.
Fix a possible dead lock when opening a file when one is already playing.

Easily reproducible with madVR.

Ticket #3865.
Update translations from Transifex:

 - Greek.