Creative: Add missing 'formspec_escape' to fix bug

Symbols used in search caused the game to hang with a grey screen,
for example searching for 'diamond;ingot'

mods/creative/init.lua

@@ -124,7 +124,7 @@ creative.set_creative_formspec = function(player, start_i)
 		tooltip[creative_clear;Reset]
 		listring[current_player;main]
 		]] ..
-		"field[0.3,3.5;2.2,1;creative_filter;;" .. inv.filter .. "]" ..
+		"field[0.3,3.5;2.2,1;creative_filter;;" .. minetest.formspec_escape(inv.filter) .. "]" ..
 		"listring[detached:creative_" .. player_name .. ";main]" ..
 		"tabheader[0,0;creative_tabs;Crafting,All,Nodes,Tools,Items;" .. tostring(inv.tab_id) .. ";true;false]" ..
 		"list[detached:creative_" .. player_name .. ";main;0,0;8,3;" .. tostring(start_i) .. "]" ..