Add validation of frame_parallel_decoding_mode

This is a boolean value that is written into bitstream, any value other
than 0 or 1 could have led to unexpected behavior. This commit fix the
issue by adding validation of the value to make sure it is boolean.

BUG=webm:1339

Change-Id: I2d3e69e8dbefcab9a0db9cb39a91a40ce531c5a1
1 file changed