Fix error caused by teleporting offline players (#12)

32affba6 re-registered stairs which have already been registered 20 lines earlier in the code, and registered them as "brick" causing the netherbrick stairs to replace Minetest's default:brick stairs. The rest of 32affba6 was already unrolled in 7a0e52da, but the stairs bug remained.

init.lua

@@ -1,4 +1,3 @@
-
 --[[
 
   Nether mod for minetest
@@ -269,20 +268,20 @@ minetest.register_abm({
 	chance = 2,
 	action = function(pos, node)
 		minetest.add_particlespawner({
-			32, --amount
-			4, --time
-			{x = pos.x - 0.25, y = pos.y - 0.25, z = pos.z - 0.25}, --minpos
-			{x = pos.x + 0.25, y = pos.y + 0.25, z = pos.z + 0.25}, --maxpos
-			{x = -0.8, y = -0.8, z = -0.8}, --minvel
-			{x = 0.8, y = 0.8, z = 0.8}, --maxvel
-			{x = 0, y = 0, z = 0}, --minacc
-			{x = 0, y = 0, z = 0}, --maxacc
-			0.5, --minexptime
-			1, --maxexptime
-			1, --minsize
-			2, --maxsize
-			false, --collisiondetection
-			"nether_particle.png" --texture
+			amount = 32,
+			time   = 4,
+			minpos = {x = pos.x - 0.25, y = pos.y - 0.25, z = pos.z - 0.25},
+			maxpos = {x = pos.x + 0.25, y = pos.y + 0.25, z = pos.z + 0.25},
+			minvel = {x = -0.8, y = -0.8, z = -0.8},
+			maxvel = {x =  0.8, y =  0.8, z =  0.8},
+			minacc = {x = 0, y = 0, z = 0},
+			maxacc = {x = 0, y = 0, z = 0},
+			minexptime = 0.5,
+			maxexptime = 1,
+			minsize    = 1,
+			maxsize    = 2,
+			collisiondetection = false,
+			texture = "nether_particle.png"
 		})
 		for _, obj in ipairs(minetest.get_objects_inside_radius(pos, 1)) do
 			if obj:is_player() then
@@ -298,6 +297,9 @@ minetest.register_abm({
 					-- teleport the player
 					minetest.after(3, function(o, p, t)
 						local objpos = o:getpos()
+						if not objpos then -- player quit the game while teleporting
+							return
+						end
 						objpos.y = objpos.y + 0.1 -- Fix some glitches at -8000
 						if minetest.get_node(objpos).name ~= "nether:portal" then
 							return
@@ -520,13 +522,6 @@ if minetest.get_modpath("moreblocks") then
 	})
 end
 
-stairs.register_stair_and_slab("brick", "nether:brick",
-	{cracky=3, oddly_breakable_by_hand=1},
-	{"nether_brick.png"},
-	"nether stair",
-	"nether slab",
-	default.node_sound_stone_defaults())
-
 
 -- Craftitems