patch 8.2.2782: Vim9: blob operations not fully tested

Problem:    Vim9: blob operations not fully tested.
Solution:   Make more blob tests run in Vim9 script.  Fix filter().  Make
            insert() give an error for a null blob, like add().

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2782,
 /**/
     2781,
 /**/