audio-io fixed no callback issue at start

audio-io fixed no callback issue at start

Changes:
 * In case of asyncronous write, never callback will be invoked when
   application has wrote less than prebuf(-1) at first callback.
   To avoid deadlock between applicaiton and pulseaudio, audio-io
   ensure to write at least size of prebuf.
 * Need to move enabling __mIsInit flag to state changed callback.
   Because of some audio-io APIs rejected at first stream callback.
   (e.g audio_out_drain, audio_out_flush, ...)

[Version] 0.3.56
[Profile] Common
[Issue Type] Compatibility

Signed-off-by: KimJeongYeon <jeongyeon.kim@samsung.com>
Change-Id: I64e43913c6a22ab2003615b40b9e616c59423628