wallet: one-shot storage commands honour -walletbackend=sqlite

-walletstorageaudit, -walletstoragecheck and -backupwallet all read
wallet.dat regardless of the selected backend. Under -walletbackend=sqlite
that is wrong, and for backup it is dangerous: it silently backs up the
stale plaintext wallet.dat instead of the live wallet.sqlite.

- ScanWalletRecords() routes to the active SQLite store instead of a
  Berkeley DB cursor (it returned an error under the runtime before). This
  is the single choke point audit and check scan through.
- WalletSQLiteRuntimeOpenReadOnly() opens wallet.sqlite for scanning
  without loading or validating records, so the pre-load diagnostics can
  inspect a wallet the loader would refuse. main_gui opens it for
  audit/check when the SQLite backend is selected (and rejects an unknown
  backend value there too).
- BackupWallet() copies wallet.sqlite (checkpoint, then the temp/old/rename
  dance; a checkpointed SQLite file is self-contained, no lsn_reset).

wallet-sqlite-encrypt self-test proves routing on a datadir where the
SQLite wallet is encrypted and wallet.dat beside it is still plaintext:
audit with the flag reports the encrypted seed, without it reports the
plaintext one; the SQLite backup carries no plaintext key and loadchecks
as a standalone wallet.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/db.h b/src/db.h
index 1a272b9..5bc94b1 100644
--- a/src/db.h
+++ b/src/db.h
@@ -368,6 +368,8 @@ bool WalletSQLiteRuntimeEraseRecord(const vector<unsigned char>& vchKey);
 bool WalletSQLiteRuntimeBeginTxn();
 bool WalletSQLiteRuntimeCommitTxn();
 void WalletSQLiteRuntimeRollbackTxn();
+bool WalletSQLiteRuntimeOpenReadOnly(const string& strPath, string& strErrorRet);
+bool WalletSQLiteRuntimeCheckpoint(string& strErrorRet);