added group_attack in cow,goat,warthog and npc

added group attack if not tamed and type(name) identical
fixed crash if unknow node in function env_damage

mods/mobs/api.lua

@@ -317,6 +317,7 @@ function mobs:register_mob(name, def)
 				local nod = minetest.get_node_or_nil(pos)
 				if not nod then return end ;  -- print ("standing in "..nod.name)
 				local nodef = minetest.registered_nodes[nod.name]
+				if not nodef then return end
 				pos.y = pos.y + 1
 
 				-- water
@@ -1185,8 +1186,10 @@ end
 				local obj = nil
 				for _, oir in pairs(minetest.get_objects_inside_radius(hitter:getpos(), 5)) do
 					obj = oir:get_luaentity()
-					if obj then
+					if obj
+					and obj.name == self.name then
 						if obj.group_attack == true
+						and not obj.tamed
 						and obj.state ~= "attack" then
 							obj.do_attack(obj, hitter, 1)
 						end

mods/mobs/cow.lua

@@ -6,6 +6,7 @@ mobs:register_mob("mobs:cow", {
 	type = "animal",
 	-- aggressive, does 5 damage to player when threatened
 	passive = false,
+	group_attack = true,
 	attack_type = "dogfight",
 	damage = 4,
 	-- health & armor

mods/mobs/goat.lua

@@ -6,6 +6,7 @@ mobs:register_mob("mobs:goat", {
 	type = "animal",
 	-- aggressive, does 5 damage to player when threatened
 	passive = false,
+	group_attack = true,
 	attack_type = "dogfight",
 	damage = 4,
 	-- health & armor

mods/mobs/npc.lua

@@ -13,6 +13,7 @@ mobs:register_mob("mobs:npc", {
 	type = "npc",
 	-- aggressive, deals 6 damage to player/monster when hit
 	passive = false,
+	group_attack = true,
 	damage = 5,					-- 3 damages if tamed
 	attack_type = "dogfight",
 	attacks_monsters = true,

mods/mobs/warthog.lua

@@ -6,6 +6,7 @@ mobs:register_mob("mobs:pumba", {
 	type = "animal",
 	-- aggressive, deals 5 damage to player when threatened
 	passive = false,
+	group_attack = true,
 	attack_type = "dogfight",
 	damage = 4,
 	-- health & armor