Avoid assertion failure in Chromaprint library

As detailed in [this beets bug](http://code.google.com/p/beets/issues/detail?id=515), the Chromaprint library fails an assertion if the sample count is not divisible by the channel count. We should check this before invoking the library.

Start by locating the Python code that invokes the Chromaprint library and inspect how sample count and channel count are passed through. Reproduce the non-divisible sample-count case described in the issue; done means the input is handled before the library call without triggering its assertion.

Written by the indexing model from the issue text.