Fix crash on GetFolderItems with no mediaId

When no media ID is given, we proceed to retrieve the
folder items for the root ID instead, but the callback
parameter was still media ID and not root ID, which
results in a mismatch if there is a timeout when
retrieving the items and lead to a crash.

Bug: 338156685
Bug: 402624784
Flag: com.android.bluetooth.flags.browsing_refactor
Test: atest BluetoothInstrumentationTests
Ignore-AOSP-First: not AOSP first anymore
Change-Id: Ia3bb5cf2babc0bc9c71c2e7bf60574501d9baac4