avoided compilation warnings on gcc 3.3.x systems

diff --git a/skeletons/INTEGER.c b/skeletons/INTEGER.c
index 0c7a81a..16a6b74 100644
--- a/skeletons/INTEGER.c
+++ b/skeletons/INTEGER.c
@@ -67,7 +67,7 @@
 	/*
 	 * Make sure we have this length.
 	 */
-	(char *)buf_ptr += rval.consumed;
+	buf_ptr = ((char *)buf_ptr) + rval.consumed;
 	size -= rval.consumed;
 	if(length > (ber_tlv_len_t)size) {
 		rval.code = RC_WMORE;