Fix handling urls without hostname

For weird URLs like "http:something" host is None but scheme is "http".
I believe we should not fail for such urls.

Before the patch we had the following exception:
```
Traceback (most recent call last):
  File "referer_parser/test/__init__.py", line 204, in test_no_host
    r = Referer("http:some/path")
  File "referer_parser/__init__.py", line 57, in __init__
    referer = self._lookup_referer(ref_host, ref_uri.path, True)
  File "referer_parser/__init__.py", line 79, in _lookup_referer
    referer = self.referers[ref_host + ref_path]
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'
```

Author: tailhook

python/referer_parser/__init__.py

@@ -41,7 +41,8 @@ def __init__(self, ref_url, curr_url=None, referers=REFERERS):
 
         ref_uri = urlparse(ref_url)
         ref_host = ref_uri.hostname
-        self.known = ref_uri.scheme in {'http', 'https'}
+        self.known = (ref_uri.scheme in {'http', 'https'} and
+                      ref_host is not None)
         self.uri = ref_uri
 
         if not self.known:
@@ -63,7 +64,7 @@ def __init__(self, ref_url, curr_url=None, referers=REFERERS):
 
         self.referer = referer['name']
         self.medium = referer['medium']
-        
+
         if referer['medium'] == 'search':
             if 'params' not in referer or not referer['params']:
                 return

python/referer_parser/test/__init__.py

@@ -23,7 +23,7 @@ def test_google_minimal(self):
         self.assertEqual(r.referer, 'Google')
         self.assertIsNone(r.search_term)
         self.assertEqual(r.medium, 'search')
-        
+
     def test_google_term(self):
         """ Google search #2
         """
@@ -115,7 +115,7 @@ def test_ask_search(self):
 dm=ctry&atb=sysid%3D406%3Aappid%3D113%3Auid%3D8f40f651e7b608b5%3Auc%3D1346336505%3Aqu%3D\
 pendulums%3Asrc%3Dcrt%3Ao%3D1921&locale=en_GB""")
         self.check_equals(r, 'Ask', 'pendulums', 'search')
-        
+
     def test_mailru_search(self):
         """ Mail.ru search
         """
@@ -184,7 +184,7 @@ def test_outlookcom_mail(self):
         """
         r = Referer("http://co106w.col106.mail.live.com/default.aspx?rru=inbox")
         self.check_no_term(r, 'Outlook.com', 'email')
-        
+
     def test_orange_webmail(self):
         """ Orange Webmail
         """
@@ -193,12 +193,21 @@ def test_orange_webmail(self):
         self.check_no_term(r, 'Orange Webmail', 'email')
 
     def test_internal(self):
-        r = Referer("http://www.snowplowanalytics.com/about/team", 
+        r = Referer("http://www.snowplowanalytics.com/about/team",
                     "http://www.snowplowanalytics.com/account/profile")
         self.assertTrue(r.known)
         self.assertEqual(r.medium, 'internal')
         self.assertIsNone(r.search_term)
         self.assertIsNone(r.referer)
 
+    def test_no_host(self):
+        r = Referer("http:some/path")
+        self.assertFalse(r.known)
+        self.assertIsNone(r.uri.hostname)
+        self.assertEqual(r.medium, 'unknown')
+        self.assertIsNone(r.search_term)
+        self.assertIsNone(r.referer)
+
+
 if __name__ == '__main__':
     unittest.main()