Add pre-read FIXME comment

servers/slapd/back-bdb/modify.c

@@ -552,6 +552,7 @@ retry:	/* transaction retry */
 		}
 		ctrls[++num_ctrls] = NULL;
 		op->o_preread = 0; /* prevent redo on retry */
+		/* FIXME: should read entry on the last retry */
 	}
 
 	/* nested transaction */