Go into case branches when productivity checking
Go into case branches when productivity checking

We were only looking inside the branches for termination checking, so
this might have missed some non-productive things.

mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm