[AES] Panic when no generator key is provided

include/crypto/aes_engine.hpp

@@ -105,6 +105,7 @@ namespace Crypto {
 		AESEngine() {}
 		void loadKeys(const std::filesystem::path& path);
 		bool haveKeys() { return keysLoaded; }
+		bool haveGenerator() { return m_generator.has_value(); }
 
 		constexpr bool hasKeyX(std::size_t slotId) {
 			if (slotId >= AesKeySlotCount) {

src/core/loader/ncch.cpp

@@ -131,6 +131,13 @@ bool NCCH::loadFromHeader(Crypto::AESEngine &aesEngine, IOFile& file, const FSIn
 				return false;
 			}
 
+			if (!aesEngine.haveGenerator()) {
+				Helpers::panic(
+					"Loading an encrypted ROM but your AES keys don't seem to provide the \"generator\" constant which Panda3DS requires for decryption\n"
+					"Please add it to your aes_keys.txt in a line like \"generator=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\" where the Xs are replaced with the actual generator constant value"
+				);
+			}
+
 			if (!gotCryptoKeys) {
 				Helpers::panic("ROM is encrypted but it seems we couldn't get either the primary or the secondary key");
 				return false;