Fix apparently ineffective processors when analysing audio (#2671).

Fix apparently ineffective processors when analysing audio (#2671).

A whole film ("DCP side") analysis would behave the same as a
single piece of content analysis if the film only had one piece
of content.

Here we also clarify that audio analysis of the whole film is different
to that for a single piece of content; for the whole film we use processors,
and for single pieces of content we do not.