Fix MediaFocusControl index management for PlayerRecord

When updating the PlayerRecord stack on playstate changes and
 media button event receiver registrations, evaluate the index
 of the stack entry to remove against the index of the last playing
 entry as this index was valid before the entry was removed.
 This affects the insertion index.

Change-Id: Iec58d2df6bcbd8f55925e9e0f9d48f698f7cf4e5