Utils: Make get_spyder_conda_channel return a tuple of None's if fails

- That's necessary to unpack its result correctly in the worker in
charge of checking if a new Spyder version is available.
- Also, improve a bit condition that checks the result of that function
in the worker.

spyder/utils/conda.py

@@ -203,7 +203,7 @@ def get_spyder_conda_channel():
     conda = find_conda()
 
     if conda is None:
-        return None
+        return None, None
 
     env = get_conda_env_path(sys.executable)
     cmdstr = ' '.join([conda, 'list', 'spyder', '--json', '--prefix', env])
@@ -213,7 +213,7 @@ def get_spyder_conda_channel():
         out = out.decode()
         out = json.loads(out)
     except Exception:
-        return None
+        return None, None
 
     for package_info in out:
         if package_info["name"] == 'spyder':

spyder/workers/updates.py

@@ -115,7 +115,7 @@ def start(self):
         elif is_anaconda():
             channel, channel_url = get_spyder_conda_channel()
 
-            if channel_url is None:
+            if channel is None or channel_url is None:
                 return
             elif channel == "pypi":
                 self.url = pypi_url