patch 8.2.2781: add() silently skips when adding to null list or blob

Problem:    Add() silently skips when adding to null list or blob.
Solution:   Give an error in Vim9 script.  Allocate blob when it is NULL like
            with list and dict.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2781,
 /**/
     2780,
 /**/