fix(zetaclient): ensure fallbackTx is not nil (#3632)

* fix(zetaclient): ensure fallbackTx is not nil

* make error check a bit more strict

Author: gartnera

zetaclient/chains/solana/signer/signer.go

@@ -317,7 +317,9 @@ func (signer *Signer) broadcastOutbound(
 		if err != nil {
 			// in case it is not failure due to nonce mismatch, replace tx with fallback tx
 			// probably need a better way to do this, but currently this is the only error to tolerate like this
-			if !strings.Contains(err.Error(), "NonceMismatch") {
+			errStr := err.Error()
+			if strings.Contains(errStr, "Error processing Instruction") && !strings.Contains(errStr, "NonceMismatch") &&
+				fallbackTx != nil {
 				tx = fallbackTx
 			}
 			logger.Warn().Err(err).Fields(lf).Msgf("SendTransactionWithOpts failed")