Use a TArray for SoundDecoder::readAll
Pass the correct size to LoadSoundVoc
Remove a redundant call
Use TArray and TMap instead of std::vector and std::map
Use a separate function to update an openal stream's volume
Remove an unused field
Show the name of unsupported sound formats with OpenAL
Simplify some branching
Fix creating effect map entries

TMap apparently doesn't clear the memory for new entries like std::map...