Merge #2906: Fix optional memo not being checked

b0bf2c2 Fix optional memo not being checked (Duddino)

Pull request description:

  Memos return Nullopt instead of empty string when empty.

ACKs for top commit: b0bf2c2
  Liquid369:
    tACK b0bf2c2
  Fuzzbawls:
    utACK b0bf2c2

Tree-SHA512: e9e6cd99edaa6d56da59abdfcc4056d2d613cad93203f47d3fc3c65763413e3eef8df50773a82f934fd5e912ae94579a71a5805f30eb00964f71ebd5eb6d271a

src/qt/transactionrecord.cpp

@@ -180,7 +180,7 @@ bool TransactionRecord::decomposeCreditTransaction(const CWallet* wallet, const
                 sub.type = TransactionRecord::RecvWithShieldedAddress;
                 sub.credit = sspkm->GetOutPointValue(wtx, out);
                 sub.memo = sspkm->GetOutPointMemo(wtx, out);
-                if (!sub.memo->empty()) {
+                if (sub.memo && !sub.memo->empty()) {
                     sub.type = TransactionRecord::RecvWithShieldedAddressMemo;
                 }
                 sub.idx = i;