Comment 0 for bug 994341

From errors.ubuntu.com:

If you click on "installed" while software-center is initializing (and the apt cache is not ready) it crashes with:

2012-05-03 18:01:16,188 - softwarecenter.db.enquire - ERROR - _get_estimate_nr_apps_and_nr_pkgs failed
Traceback (most recent call last):
  File "/scratch/egon/devel/software-center/trunk/softwarecenter/db/enquire.py", line 115, in _get_estimate_nr_apps_and_nr_pkgs
    tmp_matches = enquire.get_mset(0, len(self.db), None, xfilter)
  File "/scratch/egon/devel/software-center/trunk/softwarecenter/db/appfilter.py", line 94, in __call__
    if (not pkgname in self.cache or
  File "/scratch/egon/devel/software-center/trunk/softwarecenter/db/pkginfo_impl/aptcache.py", line 263, in __contains__
    return self._cache.__contains__(k)
AttributeError: 'NoneType' object has no attribute '__contains__'
Traceback (most recent call last):
  File "/scratch/egon/devel/software-center/trunk/softwarecenter/ui/gtk3/panes/installedpane.py", line 374, in profiled_rebuild_categorised_view
    rebuild_categorised_view()
  File "/scratch/egon/devel/software-center/trunk/softwarecenter/ui/gtk3/panes/installedpane.py", line 401, in rebuild_categorised_view
    persistent_duplicate_filter=(i > 0))
  File "/scratch/egon/devel/software-center/trunk/softwarecenter/db/enquire.py", line 317, in set_query
    self._blocking_perform_search()
  File "/scratch/egon/devel/software-center/trunk/softwarecenter/db/enquire.py", line 212, in _blocking_perform_search
    matches = enquire.get_mset(0, self.limit, None, xfilter)
  File "/scratch/egon/devel/software-center/trunk/softwarecenter/db/appfilter.py", line 94, in __call__
    if (not pkgname in self.cache or
  File "/scratch/egon/devel/software-center/trunk/softwarecenter/db/pkginfo_impl/aptcache.py", line 263, in __contains__
    return self._cache.__contains__(k)
AttributeError: 'NoneType' object has no attribute '__contains__'

Its often reported error so we need to fix it.