patch 8.2.5107: some callers of rettv_list_alloc() check for not OK

Problem:    Some callers of rettv_list_alloc() check for not OK. (Christ van
            Willegen)
Solution:   Use "==" instead of "!=" when checking the return value.
diff --git a/src/menu.c b/src/menu.c
index 95f6fae..a588674 100644
--- a/src/menu.c
+++ b/src/menu.c
@@ -2945,7 +2945,7 @@
     vimmenu_T	*menu;
     dict_T	*retdict;
 
-    if (rettv_dict_alloc(rettv) != OK)
+    if (rettv_dict_alloc(rettv) == FAIL)
 	return;
     retdict = rettv->vval.v_dict;