wallet: don't read db every time that a new WalletBatch is created

Better to perform the action only one time (during 'LoadWallet').
Where the value is being used.

Author: furszy

src/wallet/bdb.cpp

@@ -315,12 +315,6 @@ BerkeleyBatch::BerkeleyBatch(BerkeleyDatabase& database, const bool read_only, b
     env = database.env.get();
     pdb = database.m_db.get();
     strFile = fs::PathToString(database.m_filename);
-    if (!Exists(std::string("version"))) {
-        bool fTmp = fReadOnly;
-        fReadOnly = false;
-        Write(std::string("version"), CLIENT_VERSION);
-        fReadOnly = fTmp;
-    }
 }
 
 void BerkeleyDatabase::Open()

src/wallet/walletdb.cpp

@@ -885,10 +885,8 @@ DBErrors WalletBatch::LoadWallet(CWallet* pwallet)
 
     // Last client version to open this wallet, was previously the file version number
     int last_client = CLIENT_VERSION;
-    m_batch->Read(DBKeys::VERSION, last_client);
-
-    int wallet_version = pwallet->GetVersion();
-    pwallet->WalletLogPrintf("Wallet File Version = %d\n", wallet_version > 0 ? wallet_version : last_client);
+    bool has_last_client = m_batch->Read(DBKeys::VERSION, last_client);
+    pwallet->WalletLogPrintf("Wallet file version = %d, last client version = %d\n", pwallet->GetVersion(), last_client);
 
     pwallet->WalletLogPrintf("Keys: %u plaintext, %u encrypted, %u w/ metadata, %u total. Unknown wallet records: %u\n",
            wss.nKeys, wss.nCKeys, wss.nKeyMeta, wss.nKeys + wss.nCKeys, wss.m_unknown_records);
@@ -909,7 +907,7 @@ DBErrors WalletBatch::LoadWallet(CWallet* pwallet)
     if (wss.fIsEncrypted && (last_client == 40000 || last_client == 50000))
         return DBErrors::NEED_REWRITE;
 
-    if (last_client < CLIENT_VERSION) // Update
+    if (!has_last_client || last_client < CLIENT_VERSION) // Update
         m_batch->Write(DBKeys::VERSION, CLIENT_VERSION);
 
     if (wss.fAnyUnordered)