Merge bitcoin/bitcoin#26747: wallet: fix confusing error / GUI crash on cross-chain legacy wallet restore

21ad4e26ec320dcecc8961888bc82d0bb72d5ed3 test: add coverage for cross-chain wallet restore (Sebastian Falbesoner)
8c7222bda3f7136f312a6e57b76d6a2d0a114f68 wallet: fix GUI crash on cross-chain legacy wallet restore (Sebastian Falbesoner)

Pull request description:

  Restoring a wallet backup from another chain should result in a dedicated error message (we have _"Wallet files should not be reused across chains. Restart bitcoind with -walletcrosschain to override."_ for that). Unfortunately this is currently not the case for legacy wallet restores, as in the course of cleaning up the newly created wallet directory a `filesystem_error` exception is thrown due to the directory not being empty; the wallet database did indeed load successfully (otherwise we wouldn't know that the chain doesn't match) and hence BDB-related files and directories are already created in the wallet directory.

  For bitcoind, this leads to a very confusing error message:
  ```
  $ ./src/bitcoin-cli restorewallet test123 ~/.bitcoin/regtest/wallets/regtest_wallet/wallet.dat
  error code: -1
  error message: filesystem error: in remove: Directory not empty ["/home/thestack/.bitcoin/wallets/test123"]
  ```

  Even worse, the GUI crashes in such a scenario:
  ```
  libc++abi: terminating with uncaught exception of type std::__1::__fs::filesystem::filesystem_error: filesystem error: in remove: Directory not empty ["/home/thestack/.bitcoin/wallets/foobar"]
  Abort trap (core dumped)
  ```

  Fix this by simply deleting the whole folder via `fs::remove_all`. With this, the expected error message appears both for the `restorewallet` RPC call and in the GUI (as a message-box):

  ```
  $ ./src/bitcoin-cli restorewallet test123 ~/.bitcoin/regtest/wallets/regtest_wallet/wallet.dat
  error code: -4
  error message:
  Wallet loading failed. Wallet files should not be reused across chains. Restart bitcoind with -walletcrosschain to override.
  ```

ACKs for top commit:
  achow101:
    ACK 21ad4e26ec320dcecc8961888bc82d0bb72d5ed3
  aureleoules:
    ACK 21ad4e26ec320dcecc8961888bc82d0bb72d5ed3
  furszy:
    utACK 21ad4e26

Tree-SHA512: 313f6494c2fbe823bff9b975cb2d9410bb518977a1e59a5159ee9836bc012947fa50b56be0e41b1a2f50d9c0c7f4fddfdf4fbe479d8a59a6ee44bb389c804abc

0 files changed, 0 insertions, 0 deletions