dialog: Sanity checks

Add NULL checks for the parse_dlg_rr_param().
Segfault when 'did' parameter was empty in the Route header (e.g. 'did=').

modules/dialog/dlg_handlers.c

@@ -970,7 +970,29 @@ static inline int parse_dlg_rr_param(char *p, char *end, int *h_entry, int *h_id
 {
 	char *s;
 
+	/* sanity checks */
+	if (!p) {
+		LM_ERR("NULL start of parameter string");
+		return -1;
+	}
+
+	if (!end) {
+		LM_ERR("NULL end of parameter string");
+		return -1;
+	}
+
+	if (!h_entry) {
+		LM_ERR("NULL h_entry");
+		return -1;
+	}
+
+	if (!h_id) {
+		LM_ERR("NULL h_id");
+		return -1;
+	}
+
 	for ( s=p ; p<end && *p!=DLG_SEPARATOR ; p++ );
+
 	if (*p!=DLG_SEPARATOR) {
 		LM_ERR("malformed rr param '%.*s'\n", (int)(long)(end-s), s);
 		return -1;