[PATCH 2/4] my_fileno: use rb_io_check_closed for Ruby <3.1

[Eric Wong <bofh@yhbt.net>]

This is less code and hopefully smaller binaries.
`rb_io_check_closed' has been in Ruby since the pre-CVS of
decades ago, and it doesn't matter if it's removed or not
in the future since Ruby 3.1+ doesn't see this code path
and calls `rb_io_descriptor' directly.
---
 ext/raindrops/my_fileno.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/ext/raindrops/my_fileno.h b/ext/raindrops/my_fileno.h
index 646f31b..3a0100f 100644
--- a/ext/raindrops/my_fileno.h
+++ b/ext/raindrops/my_fileno.h
@@ -9,9 +9,8 @@ static int my_fileno(VALUE io)
 	rb_io_t *fptr;
 
 	GetOpenFile(io, fptr);
+	rb_io_check_closed(fptr);
 
-	if (fptr->fd < 0)
-		rb_raise(rb_eIOError, "closed stream");
 	return fptr->fd;
 }
 #endif /* Ruby <3.1 !HAVE_RB_IO_DESCRIPTOR */