msacm32/tests: Add some acmStreamPrepareHeader and acmStreamConvert tests (try 2)

[Andrew Eikum]

On Tue, Nov 24, 2015 at 05:08:00PM +0800, Bruno Jesus wrote:
> +    hdr.cbSrcLengthUsed = 12345;
> +    hdr.cbDstLengthUsed = 12345;

The rest looks OK, but I don't understand why these are set. Does the
application really set them to this value after Prepare and before
Convert? The tests seem to behave the same if I leave them at 0.

Andrew