partition: improve error reporting when reading header partition pack kl
partition: improve error reporting when reading header partition pack kl

It's not supposed to fail. If it does fail then some detail about
where it failed is useful and so reads etc. are wrapped in CHK_ORET

Limecraft/ebu-libmxf,stuarthicks/libmxf,stuarthicks/libmxf,Limecraft/ebu-libmxf,Limecraft/ebu-libmxf,stuarthicks/libmxf,stuarthicks/libmxf