Improve WAV parser

[linkyndy]

Improve WAV parser by performing a best-effort when extracting metadata from files that do not strictly follow the format spec.

This deals with a particular case when non-PCM files might not have a fact chunk defined, in which case we currently discard the entire file. With this change, we will still recognise the file as a WAV file and attempt to build all relevant metadata from the available information in the header.