[Core] Fix potential renaming unicode folders issue

- Found an issue while fixing `get_name` where `handle.rename_file`
  would raise a UnicodeDecodeError with non-ascii on Python 2. The
  fix is to catch this and pass unicode string to method instead.

- Add a test `test_rename_unicode` to verify no errors are generated.
- Updated test to use core.session instead of creating another one.

deluge/core/torrent.py

@@ -1382,7 +1382,7 @@ class Torrent(object):
             # lt needs utf8 byte-string. Otherwise if wstrings enabled, unicode string.
             try:
                 self.handle.rename_file(index, filename.encode('utf8'))
-            except TypeError:
+            except (UnicodeDecodeError, TypeError):
                 self.handle.rename_file(index, filename)
 
     def rename_folder(self, folder, new_folder):
@@ -1418,7 +1418,7 @@ class Torrent(object):
                 new_path = _file['path'].replace(folder, new_folder, 1)
                 try:
                     self.handle.rename_file(_file['index'], new_path.encode('utf8'))
-                except TypeError:
+                except (UnicodeDecodeError, TypeError):
                     self.handle.rename_file(_file['index'], new_path)
 
         def on_folder_rename_complete(dummy_result, torrent, folder, new_folder):

deluge/tests/test_torrent.py

@@ -13,7 +13,7 @@ from base64 import b64encode
 
 import mock
 from twisted.internet import reactor
-from twisted.internet.task import deferLater
+from twisted.internet.task import defer, deferLater
 from twisted.trial import unittest
 
 import deluge.component as component
@@ -24,7 +24,7 @@ from deluge.common import utf8_encode_structure, windows_check
 from deluge.core.core import Core
 from deluge.core.rpcserver import RPCServer
 from deluge.core.torrent import Torrent
-from deluge.core.torrentmanager import TorrentState
+from deluge.core.torrentmanager import TorrentManager, TorrentState
 
 from .basetest import BaseTestCase
 
@@ -44,7 +44,7 @@ class TorrentTestCase(BaseTestCase):
         self.rpcserver = RPCServer(listen=False)
         self.core = Core()
         self.core.config.config['lsd'] = False
-        self.session = lt.session()
+        self.session = self.core.session
         self.torrent = None
         return component.start()
 
@@ -304,3 +304,17 @@ class TorrentTestCase(BaseTestCase):
         handle = self.session.add_torrent(atp)
         self.torrent = Torrent(handle, {})
         self.assertEqual(self.torrent.get_name(), 'সুকুমার রায়.mkv')
+
+    def test_rename_unicode(self):
+        """Test renaming file/folders with unicode filenames."""
+        atp = self.get_torrent_atp('unicode_filenames.torrent')
+        handle = self.session.add_torrent(atp)
+        self.torrent = Torrent(handle, {})
+        # Ignore TorrentManager method call
+        TorrentManager.save_resume_data = mock.MagicMock
+
+        result = self.torrent.rename_folder('unicode_filenames', 'Горбачёв')
+        self.assertIsInstance(result, defer.DeferredList)
+
+        result = self.torrent.rename_files([[0, 'new_рбачёв']])
+        self.assertIsNone(result)