util: make EncodeBase58 consume Spans

src/qt/guiutil.cpp

@@ -94,7 +94,7 @@ static std::string DummyAddress(const CChainParams &params)
     std::vector<unsigned char> sourcedata = params.Base58Prefix(CChainParams::PUBKEY_ADDRESS);
     sourcedata.insert(sourcedata.end(), dummydata, dummydata + sizeof(dummydata));
     for(int i=0; i<256; ++i) { // Try every trailing byte
-        std::string s = EncodeBase58(sourcedata.data(), sourcedata.data() + sourcedata.size());
+        std::string s = EncodeBase58(sourcedata);
         if (!IsValidDestinationString(s)) {
             return s;
         }