apport-retrace's rebuild-package-info makes bad assumption

It seems that the --rebuild-package-info switch assumes that the report being rebuilt is from the same system which is doing the rebuilding. I say this because it calls report.py's add_package_info, but then that calls fileutils.py's find_file_package (which has no information about the report), and that in turn calls the packaging backend's get_file_package() which is a lot smarter if it is passed the release and architecture from the report. As an example consider how sandboxutils.py calls get_file_package():

92 pkg = apport.packaging.get_file_package(l, True, pkgmap_cache_dir,
93 release=report['DistroRelease'],
94 arch=report.get('Architecture'))

The best thing to do is probably call get_file_package() directly from apport-retrace but the sandbox would need to be created first. Or pass a switch that'll ensure the report's Package field is created when the sandbox is being generated.