Fix source buffer selection

This patch fixes a bug in the interaction between the recode loop and
spatial resampling. If the codec was in a spatial resampling state,
and a subsequent iteration of the recode loop disables resampling,
then the source buffer must be reset to the unscaled source.

Change-Id: I4e4cd47b943f6cd26a47449dc7f4255b38e27c77