patch 8.0.0268: may get ml_get error when :luado deletes lines

Problem:    May get ml_get error when :luado deletes lines or switches to
            another buffer. (Nikolai Pavlov, issue #1421)
Solution:   Check the buffer and line every time.

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    268,
 /**/
     267,
 /**/