patch 8.2.2585: Vim9: illegal memory access

Problem:    Vim9: illegal memory access.
Solution:   Check byte right after "null", not one more.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2585,
 /**/
     2584,
 /**/

src/vim9compile.c

@@ -4184,7 +4184,7 @@ compile_expr7(
 	 * "null" constant
 	 */
 	case 'n':   if (STRNCMP(*arg, "null", 4) == 0
-						   && !eval_isnamec((*arg)[5]))
+						   && !eval_isnamec((*arg)[4]))
 		    {
 			*arg += 4;
 			rettv->v_type = VAR_SPECIAL;