enum.c (enum_chunk): Give proper error message if no block given. cf [ruby-core:25912]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@25204 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

enum.c

@@ -2103,6 +2103,8 @@ enum_chunk(int argc, VALUE *argv, VALUE enumerable)
     VALUE initial_state;
     VALUE enumerator;
 
+    if(!rb_block_given_p())
+	rb_raise(rb_eArgError, "no block given");
     rb_scan_args(argc, argv, "01", &initial_state);
 
     enumerator = rb_obj_alloc(rb_cEnumerator);