updated for version 7.3.646
Problem:    When reloading a buffer the undo file becomes unusable unless ":w"
            is executed. (Dmitri Frank)
Solution:   After reloading the buffer write the undo file. (Christian
            Brabandt)
diff --git a/src/version.c b/src/version.c
index f30551b..2f20fa6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -720,6 +720,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    646,
+/**/
     645,
 /**/
     644,