Fix signal_get_aspect()

Had a series of bugs as result, like auto-clearing IPs and not-working lzb

advtrains_interlocking/lzb.lua

@@ -117,7 +117,6 @@ local function look_ahead(id, train)
 					idx = trav,
 					spd = lspd,
 				})
-				-- TODO register aspect change callback!
 			end
 		end
 	end
@@ -126,6 +125,8 @@ local function look_ahead(id, train)
 	lzb.travspd = travspd
 	lzb.travwspd = travwspd
 	
+	--train.debug = dump(lzb)
+	
 end
 
 --[[

advtrains_interlocking/signal_api.lua

@@ -287,7 +287,7 @@ function advtrains.interlocking.signal_get_supposed_aspect(pos)
 end
 
 -- Returns the actual aspect of the signal at position, as returned by the nodedef.
--- returns nil
+-- returns nil when there's no signal at the position
 function advtrains.interlocking.signal_get_aspect(pos)
 	local node=advtrains.ndb.get_node(pos)
 	local ndef=minetest.registered_nodes[node.name]
@@ -295,8 +295,9 @@ function advtrains.interlocking.signal_get_aspect(pos)
 		local asp = ndef.advtrains.get_aspect(pos, node)
 		if not asp then asp = DANGER end
 		fillout_aspect(asp)
-		return 
+		return asp
 	end
+	return nil
 end
 
 local players_assign_ip = {}