Initialize the Media Player list at start

If the browsable list builder fails to receive any connect callbacks when
connecting to media services, we could be left in a state where the media
player list is uninitialized. This is fixed by always initializing the
media player list at the start of AVRCP.

Change-Id: I15088c1f4e8ffa2ac8a101339c9b47989fc17a5e
Fixes: 36151636
Test: Manually tested connecting AVRCP with AVIC-8100NEX
(cherry picked from commit 11bf73ff)