audio: fix narrowing conversion errors on MSVC.
audio: fix narrowing conversion errors on MSVC.

mosra/magnum-examples,Squareys/magnum-examples,mosra/magnum-examples,Squareys/magnum-examples,Squareys/magnum-examples,mosra/magnum-examples,mosra/magnum-examples,mosra/magnum-examples,mosra/magnum-examples,mosra/magnum-examples,Squareys/magnum-examples