use strrchr to take last dot that specifies the chunk number

file might have a extension starting by dot, use strrchr to get the
last dot that specifies the chunk number

src/handler.c

@@ -113,7 +113,7 @@ int tip_client_state_process_payload(struct tip_client *cli)
 		}
 
 		/* get chunk number from file extension, e.g. FILE.0 */
-		chunk = strchr(uri, '.');
+		chunk = strrchr(uri, '.');
 		if (chunk) {
 			*chunk = '\0';
 			chunk++;