Start transaction earlier in backup restore.

Fixes #12159

app/src/main/java/org/thoughtcrime/securesms/backup/FullBackupImporter.java

@@ -97,12 +97,12 @@ public class FullBackupImporter extends FullBackupBase {
     int count = 0;
 
     SQLiteDatabase keyValueDatabase = KeyValueDatabase.getInstance(ApplicationDependencies.getApplication()).getSqlCipherDatabase();
+
+    db.beginTransaction();
+    keyValueDatabase.beginTransaction();
     try {
       BackupRecordInputStream inputStream = new BackupRecordInputStream(is, passphrase);
 
-      db.beginTransaction();
-      keyValueDatabase.beginTransaction();
-
       dropAllTables(db);
 
       BackupFrame frame;