Open the topics column when the chat list is expanded

[meh7an]

Opening a forum from the chat list shows its topics in a separate column, with the chat list narrowed to userpics on its left. Dialogs::Widget::showForum() does that through openChildList(), but only when the chat list is not collapsed. When it is collapsed, the forum is opened through changeOpenedForum(), which shows the topics in place of the chats.

That choice was not revisited when the chat list was expanded afterwards. For example, collapsing the chat list, opening a forum and then expanding the list kept the topics in place of the chats, without the chat list column that opening the same forum from the expanded list shows.

Now showForum() remembers when it was asked for a child column and fell back to changeOpenedForum() only because the chat list was collapsed. When the chat list is expanded, resizeEvent() opens the forum again in the child column. Forums opened without a child column, for example from a profile, keep their layout, and so do forums with the Hide chat list in forums option enabled.

Testing

Built and tested on macOS (Debug):

• Collapsing the chat list, opening a forum from it and expanding the list shows the chat list column next to the topics, as opening the forum from the expanded list does.
• Opening a forum from the expanded chat list is unchanged.