patch 8.1.1780: warning for file no longer available is repeated

Problem:    Warning for file no longer available is repeated every time Vim is
            focused. (Brian Armstrong)
Solution:   Only give the message once. (closes #4748)

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1780,
 /**/
     1779,
 /**/