Short circuit the case where there is nothing new
Short circuit the case where there is nothing new

Since reconfiguring can do lots of work (since it moves down the
pipeline's cluster heirarchy), we want to skip any reconfiguring which
is involved with an empty config block.

mathstuf/sprokit,linus-sherrill/sprokit,Kitware/sprokit,Kitware/sprokit,Kitware/sprokit,mathstuf/sprokit,linus-sherrill/sprokit,mathstuf/sprokit,mathstuf/sprokit,Kitware/sprokit,linus-sherrill/sprokit,linus-sherrill/sprokit