prevent NPC from mobs_redo to take environmental dammage

interface_mobs_api.lua

@@ -112,6 +112,21 @@ function yl_speak_up.do_mobs_after_activate(self, staticdata, def, dtime)
 end
 
 
+-- prevent NPC from getting hurt by special nodes
+-- This has another positive side-effect: update_tag doesn't get called constantly
+if(not(yl_speak_up.orig_do_env_damate)) then
+	yl_speak_up.orig_do_env_damate = mobs.mob_class.do_env_damage
+end
+mobs.mob_class.do_env_damage = function(self)
+	-- we are only responsible for talking NPC
+	if(not(self) or not(self.yl_speak_up)) then
+		return yl_speak_up.orig_mobs_update_tag(self)
+	end
+	-- *no* env dammage for NPC
+	return
+end
+
+
 -- we need to override this function from mobs_redo mod so that color
 -- changes to the name tag color are possible
 -- BUT: Only do this once. NOT at each reset!