avoid empty line in return undefined

Author: bobzhang

jscomp/core/js_dump.ml

@@ -1212,6 +1212,8 @@ and function_body (cxt : cxt) f (b : J.block) : unit =
               : cxt)
       | Return { expression_desc = Undefined } -> ()
       | _ -> ignore (statement false cxt f s : cxt))
+  | [ s; { statement_desc = Return { expression_desc = Undefined } } ] ->
+      ignore (statement false cxt f s : cxt)
   | s :: r ->
       let cxt = statement false cxt f s in
       P.newline f;
@@ -1225,8 +1227,7 @@ and brace_block cxt f b =
 and statements top cxt f b =
   iter_lst cxt f b
     (fun cxt f s -> statement top cxt f s)
-    (if top then P.at_least_two_lines
-    else P.newline)
+    (if top then P.at_least_two_lines else P.newline)
 
 let string_of_block (block : J.block) =
   let buffer = Buffer.create 50 in