config: Support UTF-8 in default config

Fixes issue reported at https://discuss.mopidy.com/t/428.

Mopidy-HTTP-Kuechenradio includes a non-ASCII UTF-8 character in its
default config. If Mopidy didn't already have a config file, it crashed
when trying to create the initial config file based on the default
config of all available extensions.

docs/changelog.rst

@@ -10,6 +10,12 @@ v0.19.5 (UNRELEASED)
 
 Bug fix release.
 
+- config: Support UTF-8 in default config. If an extension with non-ASCII
+  characters in its default config was installed, and Mopidy didn't already
+  have a config file, Mopidy would crashed when trying to create the initial
+  config file based on the default config of all available extensions.
+  (Fixes: :discuss:`428`)
+
 - Models: Hide empty collections from :func:`repr()` representations.
 
 - Models: Field values are no longer stored on the model instance when the

mopidy/config/__init__.py

@@ -97,8 +97,12 @@ def format_initial(extensions):
     versions = ['Mopidy %s' % versioning.get_version()]
     for extension in sorted(extensions, key=lambda ext: ext.dist_name):
         versions.append('%s %s' % (extension.dist_name, extension.version))
-    description = _INITIAL_HELP.strip() % {'versions': '\n#   '.join(versions)}
-    return description + '\n\n' + _format(config, {}, schemas, False, True)
+
+    header = _INITIAL_HELP.strip() % {'versions': '\n#   '.join(versions)}
+    formatted_config = _format(
+        config=config, comments={}, schemas=schemas,
+        display=False, disable=True).decode('utf-8')
+    return header + '\n\n' + formatted_config
 
 
 def _load(files, defaults, overrides):