Better parcel parsing in MediaMetadataRetriver

parcel parsing during SET_DATA_SOURCE_URL pulled a count and
blindly assumed there was that much data. Check that we successfully
get data from the parcel, complaining if not.

Also cleaned up a 32/64 bit inconsistency in how much data was put into
the parcel.

Bug: 132274514
Test: poc
Change-Id: I4d2c398906176b383426e96ba91f49547d327843