wallet: List sqlite wallets with empty string name

Although it is not explicitly possible to create a default wallet with
descriptors, it is possible to migrate a default wallet and have it end
up being a default wallet with descriptors. These wallets should be
listed by ListDatabases so that it appears in wallet directory listings
to avoid user confusion.

Author: achow101

src/wallet/db.cpp

@@ -42,12 +42,12 @@ std::vector<fs::path> ListDatabases(const fs::path& wallet_dir)
                 (IsBDBFile(BDBDataFile(it->path())) || IsSQLiteFile(SQLiteDataFile(it->path())))) {
                 // Found a directory which contains wallet.dat btree file, add it as a wallet.
                 paths.emplace_back(path);
-            } else if (it.depth() == 0 && it->symlink_status().type() == fs::file_type::regular && IsBDBFile(it->path()) && it->path().extension() != ".bak") {
+            } else if (it.depth() == 0 && it->symlink_status().type() == fs::file_type::regular && it->path().extension() != ".bak") {
                 if (it->path().filename() == "wallet.dat") {
                     // Found top-level wallet.dat btree file, add top level directory ""
                     // as a wallet.
                     paths.emplace_back();
-                } else {
+                } else if (IsBDBFile(it->path())) {
                     // Found top-level btree file not called wallet.dat. Current bitcoin
                     // software will never create these files but will allow them to be
                     // opened in a shared database environment for backwards compatibility.

test/functional/wallet_migration.py

@@ -539,6 +539,7 @@ def test_default_wallet(self):
         assert_equal(info["format"], "sqlite")
 
         walletdir_list = wallet.listwalletdir()
+        assert {"name": info["walletname"]} in walletdir_list["wallets"]
 
         # Check backup existence and its non-empty wallet filename
         backup_filename = f"default_wallet_{curr_time}.legacy.bak"