Fix duplicate subtitle widget in group call panel

Move setupMembers() before _subtitle.create() to prevent re-entrancy.
The rpl chain inside _subtitle.create() can fire synchronously during
FlatLabel construction, calling setupMembers() which triggers geometry
updates that re-enter refreshTitle(). Since object_ptr::create() has
not yet assigned the new widget, _subtitle appears null and a second
subtitle is created.

Author: paterkleomenis

Telegram/SourceFiles/calls/group/calls_group_panel.cpp

@@ -2901,6 +2901,9 @@ void Panel::refreshTitle() {
 	}
 	refreshTitleGeometry();
 	if (!_subtitle && mode() == PanelMode::Default) {
+		if (!_members) {
+			setupMembers();
+		}
 		_subtitle.create(
 			widget(),
 			rpl::single(