Add missing SetupGeneration error handling in EncryptWallet

Suggested https://github.com/bitcoin/bitcoin/pull/17304#discussion_r341286026
by me

src/wallet/wallet.cpp

@@ -572,7 +572,9 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
         // if we are using HD, replace the HD seed with a new one
         if (auto spk_man = m_spk_man.get()) {
             if (spk_man->IsHDEnabled()) {
-                spk_man->SetupGeneration(true);
+                if (!spk_man->SetupGeneration(true)) {
+                    return false;
+                }
             }
         }
         Lock();