fix segfault

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@2296 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/switch_event.c

@@ -441,9 +441,11 @@ SWITCH_DECLARE(switch_status_t) switch_event_add_body(switch_event_t *event, cha
 	char data[2048];
 
 	va_list ap;
-	va_start(ap, fmt);
-	vsnprintf(data, sizeof(data), fmt, ap);
-	va_end(ap);
+	if (fmt) {
+		va_start(ap, fmt);
+		vsnprintf(data, sizeof(data), fmt, ap);
+		va_end(ap);
+	}
 
 	if (ret == -1) {
 		return SWITCH_STATUS_MEMERR;