Script: Only log each string parameter warning message once

src/script/script_storage.hpp

@@ -16,6 +16,7 @@
 #include "../group.h"
 #include "../goal_type.h"
 #include "../story_type.h"
+#include "../3rdparty/robin_hood/robin_hood.h"
 
 #include "table/strings.h"
 #include <vector>
@@ -66,6 +67,8 @@ private:
 	void *event_data;                ///< Pointer to the event data storage.
 	void *log_data;                  ///< Pointer to the log data storage.
 
+	robin_hood::unordered_node_set<std::string> seen_unique_log_messages; ///< Messages which have already been logged once and don't need to be logged again
+
 public:
 	ScriptStorage() :
 		mode              (nullptr),