Remove nFileVersion from CWalletScanState

nFileVersion is not the actual file version and is not used except
in one place. So it is removed from CWalletScanState and changed so
that it is just read at the place it is needed. Furthermore, the
"version" record now only indicates the version of the highest
versioned client that has opened a wallet file so the variable
name is changed accordingly

Author: achow101

src/wallet/walletdb.cpp

@@ -165,7 +165,6 @@ class CWalletScanState {
     unsigned int m_unknown_records{0};
     bool fIsEncrypted{false};
     bool fAnyUnordered{false};
-    int nFileVersion{0};
     std::vector<uint256> vWalletUpgrade;
 
     CWalletScanState() {
@@ -376,12 +375,6 @@ ReadKeyValue(CWallet* pwallet, CDataStream& ssKey, CDataStream& ssValue,
 
             pwallet->LoadKeyPool(nIndex, keypool);
         }
-        else if (strType == "version")
-        {
-            ssValue >> wss.nFileVersion;
-            if (wss.nFileVersion == 10300)
-                wss.nFileVersion = 300;
-        }
         else if (strType == "cscript")
         {
             uint160 hash;
@@ -419,7 +412,7 @@ ReadKeyValue(CWallet* pwallet, CDataStream& ssKey, CDataStream& ssValue,
                 return false;
             }
         } else if (strType != "bestblock" && strType != "bestblock_nomerkle" &&
-                strType != "minversion" && strType != "acentry") {
+                strType != "minversion" && strType != "acentry" && strType != "version") {
             wss.m_unknown_records++;
         }
     } catch (...)
@@ -512,7 +505,11 @@ DBErrors WalletBatch::LoadWallet(CWallet* pwallet)
     if (result != DBErrors::LOAD_OK)
         return result;
 
-    pwallet->WalletLogPrintf("nFileVersion = %d\n", wss.nFileVersion);
+    // Last client version to open this wallet, was previously the file version number
+    int last_client = CLIENT_VERSION;
+    ReadVersion(last_client);
+
+    pwallet->WalletLogPrintf("nFileVersion = %d\n", 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);
@@ -525,10 +522,10 @@ DBErrors WalletBatch::LoadWallet(CWallet* pwallet)
         WriteTx(pwallet->mapWallet.at(hash));
 
     // Rewrite encrypted wallets of versions 0.4.0 and 0.5.0rc:
-    if (wss.fIsEncrypted && (wss.nFileVersion == 40000 || wss.nFileVersion == 50000))
+    if (wss.fIsEncrypted && (last_client == 40000 || last_client == 50000))
         return DBErrors::NEED_REWRITE;
 
-    if (wss.nFileVersion < CLIENT_VERSION) // Update
+    if (last_client < CLIENT_VERSION) // Update
         WriteVersion(CLIENT_VERSION);
 
     if (wss.fAnyUnordered)