introduce libwebsocket_is_final_fragment

Signed-off-by: Andy Green <andy@warmcat.com>
diff --git a/lib/libwebsockets.c b/lib/libwebsockets.c
index 0775fad..eb9cc85 100644
--- a/lib/libwebsockets.c
+++ b/lib/libwebsockets.c
@@ -2717,3 +2717,9 @@
 
 	return n;
 }
+
+int
+libwebsocket_is_final_fragment(struct libwebsocket *wsi)
+{
+	return wsi->final;
+}