Call DownloadStats.finish() when done

Previously we relied on DownloadStats.report() to do it, but we don't
guarantee that will happen anymore. And really, when
Downloader.update_cache or Downloader.download_for_time finish, it's
done and should be marked as such.

csppfetch/__init__.py

@@ -960,6 +960,7 @@ class Downloader:
             retries = 1
         stats = DownloadStatistics(progress=progress)
         self.download_first_available(filesets, dst, timeout=timeout, retries=retries, retry_wait=retry_wait, do_download = do_download, download_stats = stats)
+        stats.finish()
         return stats
 
 
@@ -1005,6 +1006,7 @@ class Downloader:
                 # We just keep trucking on; missed files are unfortunate,
                 # but not much we can do.
                 pass
+        download_stats.finish()
         return download_stats