client: Simplify error return logic
client: Simplify error return logic

This small change makes it explicit that the returned error at this
point cannot be non-nil, because there is already a guard clause a
couple lines up. Thus, any code that mutates the error can safely do so
within the guard clause, and doesn't have to worry about errors thrown
after that block.

kklin/kelda,kelda/kelda,ejj/quilt-dev,LuiseV/quilt,kayousterhout/quilt,NetSys/quilt,kklin/quilt,ejj/quilt-dev,kayousterhout/quilt,kklin/kelda,kklin/kelda,LuiseV/quilt,quilt/quilt,ejj/quilt-dev,NetSys/quilt,LuiseV/quilt,kklin/quilt,ejj/quilt-dev,kklin/quilt,quilt/quilt,kklin/kelda,quilt/quilt,NetSys/quilt,kelda/kelda,LuiseV/quilt,LuiseV/quilt,NetSys/quilt,NetSys/quilt,kelda/kelda,kayousterhout/quilt,kelda/kelda,quilt/quilt,kklin/quilt,kayousterhout/quilt