wallet: do not encrypt wallets with disabled private keys

src/wallet/rpcwallet.cpp

@@ -2124,6 +2124,10 @@ static UniValue encryptwallet(const JSONRPCRequest& request)
     auto locked_chain = pwallet->chain().lock();
     LOCK(pwallet->cs_wallet);
 
+    if (pwallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
+        throw JSONRPCError(RPC_WALLET_ENCRYPTION_FAILED, "Error: wallet does not contain private keys, nothing to encrypt.");
+    }
+
     if (pwallet->IsCrypted()) {
         throw JSONRPCError(RPC_WALLET_WRONG_ENC_STATE, "Error: running with an encrypted wallet, but encryptwallet was called.");
     }

test/functional/wallet_createwallet.py

@@ -92,7 +92,7 @@ class CreateWalletTest(BitcoinTestFramework):
         assert_raises_rpc_error(-4, "Error: This wallet has no available keys", w5.getnewaddress)
         assert_raises_rpc_error(-4, "Error: This wallet has no available keys", w5.getrawchangeaddress)
         # Encrypt the wallet
-        w5.encryptwallet('pass')
+        assert_raises_rpc_error(-16, "Error: wallet does not contain private keys, nothing to encrypt.", w5.encryptwallet, 'pass')
         assert_raises_rpc_error(-4, "Error: This wallet has no available keys", w5.getnewaddress)
         assert_raises_rpc_error(-4, "Error: This wallet has no available keys", w5.getrawchangeaddress)