fixed wav file reading to account for extra bytes in some format chunks

Reading some wav files causes a crash as `myDataSize` is read from the wrong position. On little endian machines (e.g. Intel), this normally results in a malloc error.

The fix uses `mySubChunk1Size` (previously unused) to account for the possible 2 extra bytes at the end of the format chunk, which seem to be present it many modern wav files.