Window size: use 1024x600 to avoid a smaller UI

The change from 800x600 to 1024x576 (16:9) was a reduction in height which caused
user interface to become smaller.
Continue to use width 1024 as it is a common small screen width.

minetest.conf.example

@@ -558,7 +558,7 @@
 
 #    Height component of the initial window size.
 #    type: int
-# screen_h = 576
+# screen_h = 600
 
 #    Save window size automatically when modified.
 #    type: bool