io.c (rb_io_fwrite): set path to NULL

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@7395 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -466,7 +466,7 @@ rb_io_fwrite(ptr, len, f)
     of.f = f;
     of.f2 = NULL;
     of.mode = FMODE_WRITABLE;
-    of.path = "(rb_io_fwrite)";
+    of.path = NULL;
     return io_fwrite(ptr, len, &of);
 }