Game Events: fixed a few oversights in 056d7ac

* Fixed assertion failure when removing single-use custom events. Not actually something
  broken, I just forgot to add a "not already disabled" check when doing so since I added
  that assertion in event_handler::disable.
* Added a message to the aforementioned assertion.
* Ensure handler cleanup actually happens when removing custom events.
* Account for events with multiple names in cleanup.

src/game_events/handlers.cpp

@@ -57,11 +57,10 @@ event_handler::event_handler(const config& cfg, bool imi)
 
 void event_handler::disable()
 {
-	assert(!disabled_);
+	assert(!disabled_ && "Trying to disable a disabled event. Shouldn't happen!");
 	disabled_ = true;
 }
 
-
 void event_handler::handle_event(const queued_event& event_info, game_lua_kernel& lk)
 {
 	if(disabled_) {

src/game_events/manager_impl.cpp

@@ -149,14 +149,15 @@ void event_handlers::remove_event_handler(const std::string& id)
 	if(find_it != id_map_.end()) {
 		handler_ptr handler = find_it->second.lock();
 
-		// Remove handler.
-		if(handler) {
+		if(handler && !handler->disabled()) {
 			handler->disable();
 		}
 
 		// Do this even if the lock failed.
-		// The index by name will self-adjust later. No need to adjust it now.
 		id_map_.erase(find_it);
+
+		// Remove handler from other lists.
+		clean_up_expired_handlers(handler->get_config()["name"]);
 	}
 
 	log_handlers();
@@ -171,10 +172,13 @@ void event_handlers::clean_up_expired_handlers(const std::string& event_name)
 
 	active_.erase(to_remove, active_.end());
 
-	// Then remove any now-unlockable weak_ptrs from tbe by-name list.
-	get(event_name).remove_if(
-		[](weak_handler_ptr ptr) { return ptr.expired(); }
-	);
+	// Then remove any now-unlockable weak_ptrs from the by-name list.
+	// Might be more than one so we split.
+	for(const std::string& name : utils::split(event_name)) {
+		get(name).remove_if(
+			[](weak_handler_ptr ptr) { return ptr.expired(); }
+		);
+	}
 
 	// And finally remove any now-unlockable weak_ptrs from the with-variables name list.
 	dynamic_.remove_if(