luacheck fix and upstream check of register_protector

.luacheckrc

@@ -16,5 +16,5 @@ read_globals = {
 
 	-- deps
 	"default", "mesecon", "hb",
-	"screwdriver", "areas"
+	"screwdriver", "areas", "protector"
 }

protector.lua

@@ -115,12 +115,12 @@ function minetest.is_protected(pos, digger)
 	return old_is_protected(pos, digger)
 end
 
-if has_protector_mod then
+if has_protector_mod and protector.tool.register_protector then
 	protector.tool:register_protector('priv_protector:protector', {
 		nodes = nil, -- Compatible nodes for protector tool, uses same on_place, radius, etc.
 		param2 = nil, -- Default param2 for protector
 		on_place = nil, -- on_place callback, protector is about to be placed
-		after_place = function(user, meta, src_meta, nodename)
+		after_place = function(user, meta, src_meta)
 			-- copy members across if holding sneak when using tool
 			if user:get_player_control().sneak then
 				-- get priv on source protector / set target protector metadata