Fixbug where we suppress the exception if download fails while wait_for_status.

This exception will happen if the download RPC fails making _staging_dir = None
after Cleanup is invoked and GetStatusOfBackgroundDownloads is being called.

Bug was introduced in: Ic73a9ca0fbfd66c8ee79b8848dd019c0fca5d7d9

BUG=None
TEST=Pylint + unittest

Change-Id: I8fc2be04e21b673267ff4d0b6249e62080ce3e1b
Reviewed-on: https://gerrit.chromium.org/gerrit/34379
Tested-by: Chris Sosa <sosa@chromium.org>
Reviewed-by: Alex Miller <milleral@chromium.org>
Commit-Ready: Chris Sosa <sosa@chromium.org>
1 file changed