Fix OpenAL clear buffer.
Fix OpenAL clear buffer.

mammadori/pyglet,oktayacikalin/pyglet,mammadori/pyglet,theblacklion/pyglet,oktayacikalin/pyglet,theblacklion/pyglet,oktayacikalin/pyglet,theblacklion/pyglet,theblacklion/pyglet,oktayacikalin/pyglet,mammadori/pyglet,mammadori/pyglet,theblacklion/pyglet,oktayacikalin/pyglet