parse.y: fix parser_yyerror

* parse.y (parser_yyerror): fix buffer overflow at truncation of
  error line.  [ruby-core:81790] [Bug #13687]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59188 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_parse.rb

@@ -1001,6 +1001,12 @@ x = __ENCODING__
     end;
   end
 
+  def test_unexpected_token_error
+    assert_raise(SyntaxError) do
+      eval('"x"xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx')
+    end
+  end
+
 =begin
   def test_past_scope_variable
     assert_warning(/past scope/) {catch {|tag| eval("BEGIN{throw tag}; tap {a = 1}; a")}}