Fix field factory blocking regular build options

The check in line 265 treated field build options like a map, but
it was actually an array. There are ~120 units there so anything
with a unitDefID below 120 was not buildable by Support Comms.

The only way this worked is that the engine happens to assign defs
IDs alphabetically, and all vanilla buildings happen to have names
above 120 (mostly thanks to the many dynamic commander def clones).

Author: sprunk

LuaRules/Gadgets/unit_field_factory.lua

@@ -103,7 +103,7 @@ do
 			for j = 1, #buildList do
 				local buildDefID = buildList[j]
 				if not alreadyAdded[buildDefID] then
-					fieldBuildOpts[#fieldBuildOpts + 1] = buildDefID
+					fieldBuildOpts[buildDefID] = true
 					alreadyAdded[buildDefID] = true
 				end
 			end
@@ -271,8 +271,8 @@ function gadget:UnitCreated(unitID, unitDefID)
 	end
 	isFieldFac[unitID] = true
 	local previousUnit = Spring.GetUnitRulesParam(unitID, "fieldFactoryUnit")
-	for i = 1, #fieldBuildOpts do
-		RemoveUnit(unitID, fieldBuildOpts[i])
+	for unitDefID in pairs(fieldBuildOpts) do
+		RemoveUnit(unitID, unitDefID)
 	end
 	if previousUnit then
 		AddUnit(unitID, previousUnit)