Prevent glass slabs from becoming transparent on sides/bottom.

For all glasslike drawtype nodes, the tiles contain up to 2
textures. The second texture is for "connected" glass, but that
likely is a transparent texture. If we use the `tiles` def without
modification, we will make all those slabs/slopes transparent on all
sides except the top.

To fix, we remove the tiles[2] from the tiledef in case the node is
a glasslike drawtype.

stairsplus/registrations.lua

@@ -44,12 +44,18 @@ for _, name in pairs(default_nodes) do
 		if type(ndef.drop) == "string" then
 			drop = ndef.drop:sub(9)
 		end
+
+		local tiles = ndef.tiles
+		if #ndef.tiles > 1 and ndef.drawtype:find("glass") then
+			tiles = { ndef.tiles[1] }
+		end
+
 		stairsplus:register_all("moreblocks", name, nodename, {
 			description = ndef.description,
 			drop = drop,
 			groups = ndef.groups,
 			sounds = ndef.sounds,
-			tiles = ndef.tiles,
+			tiles = tiles,
 			sunlight_propagates = true,
 			light_source = ndef.light_source
 		})