Don't always crash generating payloads if Django is installed but not configured

CHANGELOG.md

@@ -55,6 +55,8 @@
   to be deduplicated when sending public payloads to remote ActivityPub servers. Refetching
   profiles should now fix this. ([related issue](https://git.feneas.org/jaywink/federation/issues/124))  
 
+* Don't always crash generating payloads if Django is installed but not configured.
+
 ## [0.19.0] - 2019-12-15
 
 ### Added

federation/utils/django.py

@@ -18,7 +18,11 @@ def get_configuration():
         # TODO remove or default to True once AP support is more ready
         "activitypub": False,
     }
-    configuration.update(settings.FEDERATION)
+    try:
+        configuration.update(settings.FEDERATION)
+    except ImproperlyConfigured:
+        # Django is not properly configured, return defaults
+        return configuration
     if not all([
         "get_private_key_function" in configuration,
         "get_profile_function" in configuration,