Cleanup loop termination logic in AudioRecord::obtainBuffer()

Apply the same change to AudioRecord, that was already done for AudioTrack in this CL:
    > Change-Id: I0fc48117946364cb255afd653195498891f622bd

If the proxy->obtainBuffer at the end of the "do" loop fails with status
DEAD_OBJECT, and the restoreRecord_l during the next trip of the "do"
loop also fails, then the value of the buffer fields will be based on
the previous proxy->obtainBuffer that returned DEAD_OBJECT.  This will
have cleared the buffer, but it's tricky.  So instead explicitly clear
the buffer after restoreRecord_l, before breaking out of the loop.

Change-Id: Ifc97f2ab7b8195d6b149502bb5d765d2983b07be