set o_callback to NULL for read entry callback, avoids crash in replog callback

servers/slapd/result.c

@@ -1431,6 +1431,7 @@ int slap_read_controls(
 	myop = *op;
 	myop.o_bd = NULL;
 	myop.o_res_ber = ber;
+	myop.o_callback = NULL;
 
 	rc = slap_send_search_entry( &myop, rs );
 	if( rc ) return rc;