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When an AudioPlayer is created, its playstate is set to STOPPED
 three times. A stop command is translated into a pause + seek(0).
 When a seek is underway, any new seek command was postponed. So
 when playback would start after a first seek(0), the other seeks
 would be executed, causing the stutterring.
This CL verifies that, when seeking to a certain time, any new
 seek command to the same point in time received while seeking
 is ignored.
It also correct the update of mStateFlags, which should be done
 BEFORE the command is issued to the player, in case the seek
 complete notification happens syncronously with the seek command.

This CL does NOT fix why a newly created player sees its playstate
 updated to STOPPED three times in a test app like slesTest_playUri
 before playback starts.

Change-Id: Ic7627678735f559b911ea3c5a0e1e00d7d7534d2