When converting a non-void-returning closure to a contextual function type that returns void, increase the function conversion score count. This ensures that, in the case of overload resolution, we don't accidentally favor a void-returning function over a better (or exact) fit. (rdar://problem/19776288)

Swift SVN r25140

lib/Sema/CSSimplify.cpp

@@ -1957,6 +1957,7 @@ ConstraintSystem::matchTypes(Type type1, Type type2, TypeMatchKind kind,
       
       while (!parts.empty()) {
         if (parts.back().getKind() == ConstraintLocator::ClosureResult) {
+          increaseScore(SK_FunctionConversion);
           return SolutionKind::Solved;
         }
         parts.pop_back();