Merge pull request #6055 from nextcloud/backport/6053/stable-3.9

[stable-3.9] once we call done on a sync file item, return is needed

src/libsync/propagatedownload.cpp

@@ -1226,6 +1226,7 @@ void PropagateDownloadFile::downloadFinished()
             QString error;
             if (!propagator()->createConflict(_item, _associatedComposite, &error)) {
                 done(SyncFileItem::SoftError, error, ErrorCategory::GenericError);
+                return;
             } else {
                 previousFileExists = false;
             }