(svn r27591) [1.6] -Backport from trunk:

- Change: Performance improvement for dedicated servers by skipping drawing calls earlier in the process [FS#6402] (r27579)
- Fix: Vehicles could not be hidden from the purchase list when they were in exclusive preview [FS#6454] (r27578)
- Fix: Dock and roadstop picker, client list and town authority window did not auto-resize according to their content when they were positioned at the bottom of the screen [FS#6386] (r27577)
- Fix: Various incorrect but uncritical size computations in the content client [FS#6449] (r27576, r27570)

src/window.cpp

@@ -3179,6 +3179,10 @@ void UpdateWindows()
 		w->ProcessHighlightedInvalidations();
 	}
 
+	/* Skip the actual drawing on dedicated servers without screen.
+	 * But still empty the invalidation queues above. */
+	if (_network_dedicated) return;
+
 	static int we4_timer = 0;
 	int t = we4_timer + 1;