libmedia: Initialize mState/mActive value to avoid possible crash

If track creation fails on server side, mState/mActive is left
unitialized. After this a crash can happen when track stop()
is called because of a reference to a NULL object.
Initialize mState/mActive to specific value in initialized list
of track constructor.

Change-Id: If8c3611e3229c0c1b14b81285e07b9357fec7658
CRs-Fixed: 992608