wav: Make sure the data size is a multiple of blockalign, not an exact match.

I _think_ this is a right thing to do; it fixes a .wav file I have here that
has blockalign==2 when channels==2 and bitspersample==16, which otherwise
would fail.

--HG--
extra : rebase_source : 15f20b3a49cba4497659938f0cadf92a8e23902f
1 file changed