wallet: Prevent segfault when sending to unspendable witness

src/script/standard.cpp

@@ -114,6 +114,7 @@ bool Solver(const CScript& scriptPubKey, txnouttype& typeRet, std::vector<std::v
             vSolutionsRet.push_back(std::move(witnessprogram));
             return true;
         }
+        typeRet = TX_NONSTANDARD;
         return false;
     }