Merge bitcoin#25383: wallet: don't read db every time that a new 'WalletBatch' is created

c318211 walletdb: fix last client version update (furszy)
bda8ebe wallet: don't read db every time that a new WalletBatch is created (furszy)

Pull request description:

  Found it while was working on bitcoin#25297.

  We are performing a db read operation every time that a new `WalletBatch` is created, inside the constructor, just to check if the client version field is inside the db or not.

  As the client version field does not change in the entire db lifecycle, this operation can be done only once: The first time that the db is accessed/opened and the client version value can be cached.

ACKs for top commit:
  achow101:
    ACK c318211
  w0xlt:
    reACK bitcoin@c318211

Tree-SHA512: 7fb780c656e169e8eb21e7212242494a647f6506d6da2cca828703713d440d29c82bec9e7d2c410f37b49361226ccd80846d3eeb8168383d0c2a11d85d73bee2

Author: MacroFake

src/wallet/bdb.cpp

@@ -324,12 +324,6 @@ BerkeleyBatch::BerkeleyBatch(BerkeleyDatabase& database, const bool read_only, b
     env = database.env.get();
     pdb = database.m_db.get();
     strFile = database.strFile;
-    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

@@ -879,12 +879,10 @@ DBErrors WalletBatch::LoadWallet(CWallet* pwallet)
     if (result != DBErrors::LOAD_OK)
         return result;
 
-    // Last client version to open this wallet, was previously the file version number
+    // Last client version to open this wallet
     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 total; Watch scripts: %u; HD PubKeys: %u; Metadata: %u; Unknown wallet records: %u\n",
            wss.nKeys, wss.nCKeys, wss.nKeys + wss.nCKeys,
@@ -906,7 +904,7 @@ 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)