io.c: convert to string at writev

* io.c (io_fwritev): needs conversion to string before accessing
  the content, as well as single argument case, not to segfault.
  [Feature #9323]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60534 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -1590,7 +1590,7 @@ io_fwritev(int argc, VALUE *argv, rb_io_t *fptr)
     tmp_array = ALLOCV_N(VALUE, v2, argc);
 
     for (i = 0; i < argc; i++) {
-	str = argv[i];
+	str = rb_obj_as_string(argv[i]);
 	converted = 0;
 	str = do_writeconv(str, fptr, &converted);
 	if (converted)

test/ruby/test_io.rb

@@ -1270,6 +1270,10 @@ class TestIO < Test::Unit::TestCase
     end
   end
 
+  def test_write_with_multiple_nonstring_arguments
+    assert_in_out_err([], "STDOUT.write(:foo, :bar)", ["foobar"])
+  end
+
   def test_write_non_writable
     with_pipe do |r, w|
       assert_raise(IOError) do