lavf/mov: Confine 0x00000000 to raw/twos fourcc mapping to version 0 sample descriptions

Confine the 0x00000000 to 'raw '/'twos' fourcc mapping to old version 0
sound sample descriptions, since they are the only valid sample
descriptions for this type of mapping.

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
