[TrackerIcon] Fixed parse error on UTF-8 sites with non-english chars

When parsing the site's page in search for the FAVICON, the page gets opens.
The default file encoding in dependent on the running OS, and might not
be `UTF-8` on Windows.
Therefor, some trackers might not get their icon downloaded at all because of
an error:
`UnicodeDecodeError: 'charmap' codec can't decode byte 0x90 in position 2158: character maps to <undefined>`.
This fix adds a detection of file encoding using the optional `chardet` dependency, and also a test.

Closes: deluge-torrent/deluge#333
Closes: https://dev.deluge-torrent.org/ticket/3479

deluge/tests/test_tracker_icons.py

@@ -14,7 +14,6 @@ from . import common
 from .basetest import BaseTestCase
 
 common.set_tmp_config_dir()
-deluge.ui.tracker_icons.PIL_INSTALLED = False
 common.disable_new_release_check()
 
 
@@ -45,6 +44,14 @@ class TrackerIconsTestCase(BaseTestCase):
         d.addCallback(self.assertEqual, icon)
         return d
 
+    def test_get_google_ico_hebrew(self):
+        """Test that Google.co.il page is read as UTF-8"""
+        icon = TrackerIcon(common.get_test_data_file('google.ico'))
+        d = self.icons.fetch('www.google.co.il')
+        d.addCallback(self.assertNotIdentical, None)
+        d.addCallback(self.assertEqual, icon)
+        return d
+
     def test_get_google_ico_with_redirect(self):
         # google.com redirects to www.google.com
         icon = TrackerIcon(common.get_test_data_file('google.ico'))

deluge/ui/tracker_icons.py

@@ -21,6 +21,11 @@ from deluge.configmanager import get_config_dir
 from deluge.decorators import proxy
 from deluge.httpdownloader import download_file
 
+try:
+    import chardet
+except ImportError:
+    chardet = None
+
 try:
     from PIL import Image
 except ImportError:
@@ -289,7 +294,13 @@ class TrackerIcons(Component):
         :returns: a Deferred which callbacks a list of available favicons (url, type)
         :rtype: Deferred
         """
-        with open(page) as _file:
+        encoding = 'UTF-8'
+        if chardet:
+            with open(page, 'rb') as _file:
+                result = chardet.detect(_file.read())
+                encoding = result['encoding']
+
+        with open(page, encoding=encoding) as _file:
             parser = FaviconParser()
             for line in _file:
                 parser.feed(line)