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/edit.c b/src/edit.c
index 6f22b43..808aae1 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -146,7 +146,6 @@
 #ifdef FEAT_CONCEAL
     int		cursor_line_was_concealed;
 #endif
-    int		ins_completion = FALSE;
 
     // Remember whether editing was restarted after CTRL-O.
     did_restart_edit = restart_edit;
@@ -637,11 +636,8 @@
 	 * and the cursor is still in the completed word.  Only when there is
 	 * a match, skip this when no matches were found.
 	 */
-	ins_completion = ins_compl_active()
-	    && curwin->w_cursor.col >= ins_compl_col()
-	    && ins_compl_has_shown_match();
-
-	if (ins_completion && pum_wanted())
+	if (ins_compl_active() && curwin->w_cursor.col >= ins_compl_col()
+		&& ins_compl_has_shown_match() && pum_wanted())
 	{
 	    // BS: Delete one character from "compl_leader".
 	    if ((c == K_BS || c == Ctrl_H)
@@ -699,8 +695,6 @@
 		    ins_compl_delete();
 	    }
 	}
-	else if (ins_completion && !pum_wanted() && ins_compl_preinsert_effect())
-	    ins_compl_delete();
 
 	// Prepare for or stop CTRL-X mode.  This doesn't do completion, but
 	// it does fix up the text when finishing completion.