audio: Bug fix: Fill empty data even when audio is suspended
audio: Bug fix: Fill empty data even when audio is suspended

When writing is stopped on Oto's players, unexpected delaying
happens.

The ideal solution is to have APIs to suspend and resume Oto's
player, but this is not easy. For a temporary solution, write
zero values on the players when audio is suspended.

Fixes #975

hajimehoshi/ebiten,hajimehoshi/ebiten