Merge #10341: rpc/wallet: Workaround older UniValue which returns a std::string temporary for get_str

a637734 rpc/wallet: Workaround older UniValue which returns a std::string temporary for get_str (Luke Dashjr)

Tree-SHA512: 8f03f1d301f714f700bf64e259a1c986136fd1ac532f091aa97198a39c131290c320094f4fc38c774c8db4469a75437596b1d933300e4f04037abc158a252bad

Author: laanwj

src/wallet/rpcwallet.cpp

@@ -730,7 +730,8 @@ UniValue getbalance(const JSONRPCRequest& request)
     if (request.params.size() == 0)
         return  ValueFromAmount(pwallet->GetBalance());
 
-    const std::string* account = request.params[0].get_str() != "*" ? &request.params[0].get_str() : nullptr;
+    const std::string& account_param = request.params[0].get_str();
+    const std::string* account = account_param != "*" ? &account_param : nullptr;
 
     int nMinDepth = 1;
     if (request.params.size() > 1)