Fixed several problems with the sound system

[Semphriss]

Fixes #1555

This PR fixes no less than four problems I found with the sound system:

• A heavy coin hitting a wall from below or from the right will now only play sound when at the same speed required for hitting to the left or from above (a. k. a., fixed handling of negative values)
• Coins stuck in solid matter will no longer request to play a sound every single frame.
• A sound failing to pause will no longer throw the error back to the main game loop, resulting in an unexpected crash. It will rather be handled on the spot, just like playing, stopping or resuming.
• Oppositely, a sound that fails to be created will no longer silently catch the error and continue the execution normally, but instead will force the caller to handle the error and, as one can logically assume, will not store the audio for further manipulations.

I really need to do that code cleanup, I think.