Debug: Detect which frame's state first diverged after a desync

src/crashlog.h

@@ -30,6 +30,8 @@ struct DesyncExtraInfo {
 	Flags flags = DEIF_NONE;
 	const char *client_name = nullptr;
 	int client_id = -1;
+	uint32 desync_frame_seed = 0;
+	uint32 desync_frame_state_checksum = 0;
 	FILE **log_file = nullptr; ///< save unclosed log file handle here
 	DesyncDeferredSaveInfo *defer_savegame_write = nullptr;
 };