Compatibility fix for add_body() with new body.

When computing the new content-len, accept the case when there is no pre-existing body and a newly added body.
Reported by Antonis Psaras via LinkedIn

(cherry picked from commit 8054dbf)

Conflicts:
	msg_translator.c

msg_translator.c

@@ -326,8 +326,8 @@ char* clen_builder(struct sip_msg* msg, int *clen_len, int diff)
 	char *buf, * value_s;
 	int len, value, value_len;
 	str body;
-	
-	if ( (get_body(msg,&body)!=0) || body.len==0 ) {
+
+	if ( (get_body(msg,&body)!=0) ) {
 		ser_error=E_BAD_REQ;
 		LM_ERR("no message body found (missing crlf?)");
 		return 0;