Initialize f_rabuf in the raw device case. A subsequent close()

later on would try to free it, leading to a crash.

PR:		93998
Submitted by:	neel
MFC after:	1 week

lib/libstand/open.c

@@ -113,6 +113,7 @@ open(const char *fname, int mode)
     /* see if we opened a raw device; otherwise, 'file' is the file name. */
     if (file == (char *)0 || *file == '\0') {
 	f->f_flags |= F_RAW;
+	f->f_rabuf = NULL;
 	return (fd);
     }