io.c: fix comparison subject

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62147 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -6202,7 +6202,7 @@ fptr_copy_finalizer(rb_io_t *fptr, const rb_io_t *orig)
 #if defined(__CYGWIN__) || !defined(HAVE_WORKING_FORK)
     void (*const old_finalize)(struct rb_io_t*,int) = fptr->finalize;
 
-    if (old_finalize == fptr->finalize) return;
+    if (old_finalize == orig->finalize) return;
 #endif
 
     fptr->finalize = orig->finalize;