Work around for 0 valid bits

[Cocalus]

Here's an example file and what I think the fix is for #50. I zeroed the valid bits in a hexeditor on waveformatextensible-32bit-48kHz-stereo.wav to create the example. It fails the same way in my code as the example I found in the wild. It may need to get added to more tests.

[ruuda]

Thanks for opening a pull request!

It may need to get added to more tests.

Yeah, could you also add a test to specifically test that the reported bits per sample is as expected? It could be similar to this one:

https://github.com/ruuda/hound/blob/fa88d577f08370e915a5bb3af6b772de68c53e20/src/read.rs#L966-L983

[Cocalus]

I've added the requested test.

[ruuda]

Thanks!