wallet_api: catch getTxKey exception

- getTxKey method throws an exception, e.g., when user declines txKey export

src/wallet/api/wallet.cpp

@@ -1729,6 +1729,9 @@ std::string WalletImpl::getTxKey(const std::string &txid_str) const
 
     crypto::secret_key tx_key;
     std::vector<crypto::secret_key> additional_tx_keys;
+    try
+    {
+        clearStatus();
         if (m_wallet->get_tx_key(txid, tx_key, additional_tx_keys))
         {
             clearStatus();
@@ -1744,6 +1747,12 @@ std::string WalletImpl::getTxKey(const std::string &txid_str) const
             return "";
         }
     }
+    catch (const std::exception &e)
+    {
+        setStatusError(e.what());
+        return "";
+    }
+}
 
 bool WalletImpl::checkTxKey(const std::string &txid_str, std::string tx_key_str, const std::string &address_str, uint64_t &received, bool &in_pool, uint64_t &confirmations)
 {