encode: fix use of uninitialized value
encode: fix use of uninitialized value

use_dering needs to be set before being read by od_encode_coefficients.
This is not an issue for encoder_example, which explicitly sets use_dering,
but would be for other encoders using libdaala.

xiph/daala,xiph/daala,xiphmont/daala,ycho/daala,xiphmont/daala,ycho/daala,ycho/daala,HeadhunterXamd/daala,HeadhunterXamd/daala,HeadhunterXamd/daala,xiph/daala,HeadhunterXamd/daala,ycho/daala,xiph/daala,HeadhunterXamd/daala,luctrudeau/daala,xiphmont/daala,xiph/daala,luctrudeau/daala,luctrudeau/daala,xiphmont/daala,xiphmont/daala,ycho/daala,luctrudeau/daala,luctrudeau/daala