validate bip129 header on import, and fix importing unencrypted bsms files with open wallet

src/main/java/com/sparrowwallet/sparrow/AppController.java

@@ -1287,6 +1287,7 @@ public class AppController implements Initializable {
 
     private boolean attemptImportWallet(File file, SecureString password) {
         List<WalletImport> walletImporters = List.of(new ColdcardSinglesig(), new ColdcardMultisig(),
+                new Bip129(),
                 new Electrum(),
                 new SpecterDesktop(),
                 new Descriptor(),

src/main/java/com/sparrowwallet/sparrow/io/Bip129.java

@@ -235,6 +235,10 @@ public class Bip129 implements KeystoreFileExport, KeystoreFileImport, WalletExp
             }
 
             String header = reader.readLine();
+            if(header == null || !header.startsWith("BSMS")) {
+                throw new ImportException("Not a BSMS file");
+            }
+
             String descriptor = reader.readLine();
             String paths = reader.readLine();
             String address = reader.readLine();