auth_radius: safety check for r variable

src/modules/auth_radius/sterman.c

@@ -93,7 +93,7 @@ static inline int extract_avp(
 			name->s.len = p - vp->strvalue;
 			name->s.s = vp->strvalue;
 			value->n = strtol(++p, &r, 10);
-		} else if(p && p != r && !q) {
+		} else if(p && r && p != r && !q) {
 			/* int name and int vale */
 			name->n = strtol(++p, &q, 10);
 			value->n = strtol(++r, &q, 10);