fix OOS caused by undo stack missmatch

see https://gna.org/bugs/?23323 for more description

src/replay.cpp

@@ -978,7 +978,12 @@ static std::map<int, config> get_user_choice_internal(const std::string &name, c
 	//this should never change during the execution of this function.
 	const int current_side = resources::controller->current_side();
 	const bool is_mp_game = network::nconnections() != 0;
-
+	// whether sides contains a side that is not the currently active side.
+	const bool contains_other_side = !sides.empty() && (sides.size() != 1 || sides.find(current_side) == sides.end());
+	if(contains_other_side)
+	{
+		synced_context::set_is_simultaneously();
+	}
 	std::map<int,config> retv;
 	/*
 		when we got all our answers we stop.

src/synced_context.cpp

@@ -182,6 +182,11 @@ void  synced_context::reset_is_simultaneously()
 	is_simultaneously_ = false;
 }
 
+void  synced_context::set_is_simultaneously()
+{
+	is_simultaneously_ = true;
+}
+
 bool synced_context::can_undo()
 {
 	//this method should only works in a synced context.
@@ -217,8 +222,6 @@ namespace
 
 void synced_context::pull_remote_user_input()
 {
-	//we sended data over the network.
-	is_simultaneously_ = true;
 	//code copied form persist_var, feels strange to call ai::.. functions for something where the ai isn't involved....
 	//note that ai::manager::raise_sync_network isn't called by the ai at all anymore (one more reason to put it somehwere else)
 	try{
@@ -239,7 +242,7 @@ void synced_context::pull_remote_user_input()
 
 void synced_context::send_user_choice()
 {
-	is_simultaneously_ = true;
+	assert(is_simultaneously_);
 	syncmp_registry::send_user_choice();
 }
 
@@ -267,6 +270,7 @@ static void send_require_random()
 
 config synced_context::ask_server_for_seed()
 {
+	set_is_simultaneously();
 	resources::controller->increase_server_request_number();
 	std::string name = "random_seed";
 	assert(get_synced_state() == synced_context::SYNCED);

src/synced_context.hpp

@@ -108,6 +108,10 @@ class synced_context
 		sets is_simultaneously_ = false, called when entering the synced context.
 	*/
 	static void reset_is_simultaneously();
+	/*
+		sets is_simultaneously_ = true, called using a user choice that is not the currently plaing side.
+	*/
+	static void set_is_simultaneously();
 	/**
 		@return whether there were recently no methods called that prevent undoing.
 	*/