Fix Parse.byteCount in the case of unknown units

Parse.byteCount is supposed to parse numbers followed by an optional units suffix, like "1500" or "1.5M". It behaves incorrectly in the case of an unrecognized suffix ("1.5X"), returning NaN instead of null.

The first part of the patch adds tests for Parse.byteCount and Params.getByteCount, which fail:

1) Parse byte count returns null for bad inputs
  Message:
    Expected NaN to be null.
  Stack:
    Error: Expected NaN to be null.
        at Object.<anonymous> (snowflake/proxy/test/bundle.spec.js:1849:37)
  ...

The second part of the patch fixes Parse.byteCount so it doesn't fail.