TStringList.AddObject works incorrectly in the Duplicates = dupIgnore mode

Summary

The object passed to TStringList.AddObject replaces the original object of the item regardless of Duplicates = dupIgnore mode.

System Information

• Operating system: Alt Linux 10.2
• Processor architecture: x86-64
• Compiler version: trunk
• Device: Computer

Steps to reproduce

List.Sorted := True;

List.Duplicates := dupIgnore;

List.AddObject('item1', Object1);

List.AddObject('item1', Object2);

Assert(List.Objects[List.IndexOf('item1')] = Object1);

What is the current bug behavior?

The Object2 replaces the original object of the item.

What is the expected (correct) behavior?

The item keeps the Object1.

Possible fixes

Suggested patch: fpc_stringlist_patch.patch