interpretClosure: return

I believe that `ClosureDecl::interpretClosure` should return after calling the compiled version, just as `ClosureDecl::interpretMethod` does. Otherwise whenever `compiledClosure` exists, the code will essentially be executed twice: first the compiled code is called and then the closure is executed  within the interpreter.
Merge pull request #1 from curiousleo/patch-1

interpretClosure: return