initialize module-scoped context in the module-scope

[mgh]

… get erroneous warnings

• if you create multiple audio managers, the second one would find an existing context, causing it to incorrectly log an error about AudioContext being unsupported. Since the context is module-scoped, moving the initialization there avoids unnecessary checks and fixes the erroneous log.
• also fixes defered play where an audio that's paused before it loads might still play

[rogueSkib]

Looks good to me!