Show a context menu for chats you can view in a community

[meh7an]

In an opened community, right-clicking a chat under "Chats you are in" shows the chat context menu, but right-clicking a chat under "Chats you can view" did nothing. InnerWidget::contextMenuEvent() only resolved the clicked row from the chat list selection and the collapsed folder rows, so the rows of the viewable section, selected through _communitySelected, never got a menu.

Changes

• contextMenuEvent() also resolves the selected viewable row, and its menu is filled by Window::FillDialogsEntryMenu(), as for any other row.
• The other context menu actions, such as pin, archive, mute or mark as unread, are meant for chats in the chat list. For a channel the user is not in that is not in a chat list, Filler::fillContextMenuActions() now stops after Open in new window.
• updateDialogRow() also repaints viewable community rows. The row under the menu is painted as selected while the menu is open, and its highlight stayed after the menu was closed.

Testing

Built and tested on macOS (Debug):

• Right-clicking a chat under "Chats you can view" shows Open in new window, which opens the chat in a new window.
• The row is not left highlighted after the menu is closed.
• Chats under "Chats you are in" show the same menu as before.