Fixed crash if any of the mods have custom tribes

Author: johnklipi

src/Managers/Main.cs

@@ -105,6 +105,17 @@ private static void PurchaseManager_IsTribeUnlocked(ref bool __result, TribeType
 		__result = (int)type >= Plugin.AUTOIDX_STARTS_FROM || __result;
 	}
 
+	/// <summary>
+	/// Patches the steam purchase manager to unlock custom content.
+	/// </summary>
+	[HarmonyPrefix]
+	[HarmonyPatch(typeof(SteamPlatformPurchaseManager), nameof(SteamPlatformPurchaseManager.IsProductUnlocked))]
+	private static bool SteamPlatformPurchaseManager_IsProductUnlocked(ref bool __result, IAPProduct iapProduct)
+	{
+		__result = iapProduct == null;
+		return iapProduct != null;
+	}
+
 	/// <summary>
 	/// Patches the purchase manager to add custom tribes to the list of unlocked tribes.
 	/// </summary>