Adjust the width of the player list.

Make sure the list is at least as wide as the buttons. Ilor not sure
whether you want the header centred or left aligned so left it as is.

data/gui/default/window/lobby_main.cfg

@@ -476,6 +476,7 @@
 								label = _ "Help"
 							[/button]
 						{VERTICAL_SEP}
+							horizontal_grow = "true"
 							{PLAYERLISTBOX}
 						{VERTICAL_END}
 					{HORIZONTAL_END}