Give timeline docker a proper minimum height

Making it show at least two tracks, which should be enough to also see
the "you haven't added any tracks yet" text. Otherwise the user may end
up with the timeline collapsed so far that they can only see the frame
indexes, which is confusing to a new user that may not know that
something is hidden from their view.

ChangeLog

@@ -9,6 +9,7 @@ Unreleased Version 2.2.0-pre
  * Server Fix: Show an error message if listing on a certain server is not allowed.
  * Fix: Unlist sessions more reliably when terminating sessions hosted "on this computer".
  * Fix: Don't select a newly created layer when there's a default layer.
+ * Fix: Give the timeline dock a sensible minimum height. Thanks Kink for reporting.
 
 2023-12-08 Version 2.2.0-beta.11
  * Server Fix: No longer show "cannot look up one session and then join another" when joining a session with an ID alias. Thanks Kink and Fabian for finding this.

src/desktop/widgets/timelinewidget.cpp

@@ -1492,6 +1492,8 @@ void TimelineWidget::updateTracks()
 	int effectiveTrackId = nextTrackId != 0		 ? nextTrackId
 						   : currentTrackId != 0 ? currentTrackId
 												 : anyTrackId;
+	setMinimumHeight(
+		d->rowHeight * 3 + d->horizontalScroll->sizeHint().height());
 	setCurrent(effectiveTrackId, d->currentFrame, false, false);
 	updateActions();
 	updateScrollbars();