fix: Make sure to set right target when none is given

Part-of: <https://dev.funkwhale.audio/funkwhale/funkwhale/-/merge_requests/2506>

api/funkwhale_api/common/management/commands/inplace_to_s3.py

@@ -73,7 +73,9 @@ class Command(BaseCommand):
 
         self.stdout.write(f"Found {to_change.count()} uploads to update.")
 
-        target = options.get("target", options["source"])
+        target = options.get("target")
+        if target is None:
+            target = options["source"]
 
         for upl in to_change:
             upl.audio_file = str(upl.source).replace(str(prefix), str(target))