Prefer boost::optional#get_value_or over #value_or

The latter is not defined in the earliest supported version of boost,
1.47.
https://www.boost.org/doc/libs/1_47_0/libs/optional/doc/html/boost_optional/detailed_semantics.html
https://travis-ci.org/bitcoin/bitcoin/jobs/486674823

Author: Empact

src/interfaces/wallet.cpp

@@ -353,7 +353,7 @@ class WalletImpl : public Wallet
         LOCK(m_wallet.cs_wallet);
         auto mi = m_wallet.mapWallet.find(txid);
         if (mi != m_wallet.mapWallet.end()) {
-            num_blocks = locked_chain->getHeight().value_or(-1);
+            num_blocks = locked_chain->getHeight().get_value_or(-1);
             in_mempool = mi->second.InMempool();
             order_form = mi->second.vOrderForm;
             tx_status = MakeWalletTxStatus(*locked_chain, mi->second);
@@ -384,7 +384,7 @@ class WalletImpl : public Wallet
             return false;
         }
         balances = getBalances();
-        num_blocks = locked_chain->getHeight().value_or(-1);
+        num_blocks = locked_chain->getHeight().get_value_or(-1);
         return true;
     }
     CAmount getBalance() override { return m_wallet.GetBalance(); }

src/wallet/rpcdump.cpp

@@ -785,7 +785,7 @@ UniValue dumpwallet(const JSONRPCRequest& request)
     file << strprintf("# Wallet dump created by Bitcoin %s\n", CLIENT_BUILD);
     file << strprintf("# * Created on %s\n", FormatISO8601DateTime(GetTime()));
     const Optional<int> tip_height = locked_chain->getHeight();
-    file << strprintf("# * Best block at time of backup was %i (%s),\n", tip_height.value_or(-1), tip_height ? locked_chain->getBlockHash(*tip_height).ToString() : "(missing block hash)");
+    file << strprintf("# * Best block at time of backup was %i (%s),\n", tip_height.get_value_or(-1), tip_height ? locked_chain->getBlockHash(*tip_height).ToString() : "(missing block hash)");
     file << strprintf("#   mined on %s\n", tip_height ? FormatISO8601DateTime(locked_chain->getBlockTime(*tip_height)) : "(missing block time)");
     file << "\n";
 

src/wallet/wallet.cpp

@@ -1717,10 +1717,10 @@ CWallet::ScanResult CWallet::ScanForWalletTransactions(const uint256& start_bloc
         }
         ShowProgress(strprintf("%s " + _("Rescanning..."), GetDisplayName()), 100); // hide progress dialog in GUI
         if (block_height && fAbortRescan) {
-            WalletLogPrintf("Rescan aborted at block %d. Progress=%f\n", block_height.value_or(0), progress_current);
+            WalletLogPrintf("Rescan aborted at block %d. Progress=%f\n", block_height.get_value_or(0), progress_current);
             result.status = ScanResult::USER_ABORT;
         } else if (block_height && ShutdownRequested()) {
-            WalletLogPrintf("Rescan interrupted by shutdown request at block %d. Progress=%f\n", block_height.value_or(0), progress_current);
+            WalletLogPrintf("Rescan interrupted by shutdown request at block %d. Progress=%f\n", block_height.get_value_or(0), progress_current);
             result.status = ScanResult::USER_ABORT;
         }
     }
@@ -2581,7 +2581,7 @@ static bool IsCurrentForAntiFeeSniping(interfaces::Chain::Lock& locked_chain)
  */
 static uint32_t GetLocktimeForNewTransaction(interfaces::Chain::Lock& locked_chain)
 {
-    uint32_t const height = locked_chain.getHeight().value_or(-1);
+    uint32_t const height = locked_chain.getHeight().get_value_or(-1);
     uint32_t locktime;
     // Discourage fee sniping.
     //