Avoid saving remote pictures from players with ID < 2

The relaxed offset was introduced in 44af062,
but the issue it was intended to fix (non-remote pictures not
getting saved) seems to have been caused by something else,
possibly the uninitialized idx variable.

Author: tsdko

src/game_pictures.cpp

@@ -103,9 +103,8 @@ std::vector<lcf::rpg::SavePicture> Game_Pictures::GetSaveData() const {
 	// but in multiplayer we don't want to save pictures generated by other players
 	// because 1) they occupy needless space and 2) they will be immediately out of date
 	constexpr int min_pic_id = 1;
-	constexpr int min_player_id = 1;
-	// the 50 comes from the player image offset used for remote ShowPicture commands
-	const int multiplayer_pic_ids_begin = data_size + min_pic_id + (min_player_id + 1) * 50;
+	constexpr int min_player_id = 0;
+	const int multiplayer_pic_ids_begin = GetPictureIdForPlayer(min_player_id, min_pic_id);
 	save.reserve(multiplayer_pic_ids_begin);
 
 	for (const auto& pic: pictures) {