patch 8.2.1308: Vim9: accidentally using "x" causes Vim to exit

Problem:    Vim9: accidentally using "x" causes Vim to exit.
Solution:   Disallow using ":x" or "xit" in Vim9 script. (closes #6399)
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index e8e38aa..895912f 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -3176,6 +3176,9 @@
     int		vcol;
     int		empty = (curbuf->b_ml.ml_flags & ML_EMPTY);
 
+    if (not_in_vim9(eap) == FAIL)
+	return;
+
     // the ! flag toggles autoindent
     if (eap->forceit)
 	curbuf->b_p_ai = !curbuf->b_p_ai;
@@ -3317,6 +3320,9 @@
 {
     linenr_T	lnum;
 
+    if (not_in_vim9(eap) == FAIL)
+	return;
+
     if (eap->line2 >= eap->line1
 	    && u_save(eap->line1 - 1, eap->line2 + 1) == FAIL)
 	return;