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)

src/version.c

@@ -719,6 +719,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    646,
 /**/
     645,
 /**/