fix issue 2096657: Sholes: residue shutter sound heard ONCE while taking a...

fix issue 2096657: Sholes: residue shutter sound heard ONCE while taking a picture AFTER the volume is turned off.

Do not ramp volume if the first frame of a track is processed after the track was stopped.
In the case of very short sounds, the track stop request can be received by AudioFlinger just after the start request before the first frame is mixed by AudioMixer. In this case, the track is already in stopped state and initial volume is applied with a ramp for the first frame processed which should not be the case: initial volume change is always applied immediatelly.