patch 9.1.1160: Ctrl-Y does not work well with "preinsert" when completing items

Problem:  The 'preinsert' feature requires Ctrl-Y to confirm insertion,
          but Ctrl-Y only works when the popup menu (pum) is displayed.
          Without enforcing this dependency, it could lead to confusing
          behavior or non-functional features.

Solution: Modify ins_compl_has_preinsert() to check for both 'menu' and
          'menuone' flags when 'preinsert' is set. Update documentation
          to clarify this requirement. This avoids adding complex
          conditional behaviors. (glepnir)

fixes: #16728
closes: #16753

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/insexpand.c b/src/insexpand.c
index edc4265..8a6f8af 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -1985,12 +1985,15 @@
 }
 
 /*
- * Return TRUE when preinsert is set otherwise FALSE.
+ * Return TRUE when preinsert is set AND both 'menu' and 'menuone' flags
+ * are also set, otherwise return FALSE.
  */
     static int
 ins_compl_has_preinsert(void)
 {
-    return (get_cot_flags() & (COT_PREINSERT | COT_FUZZY)) == COT_PREINSERT;
+    int cur_cot_flags = get_cot_flags();
+    return (cur_cot_flags & (COT_PREINSERT | COT_FUZZY | COT_MENU | COT_MENUONE))
+	== (COT_PREINSERT | COT_MENU | COT_MENUONE);
 }
 
 /*