search: Handle packages without description

search: Handle packages without description

If a package has no description, we would crash in search. While
this should not happen, there seem to be some weird cases where
it does.

A safer way might be to make the whole parser thing safe
against this, so pkgRecords::Lookup(Desc.FileList()) works
and returns a parser where all values are empty. This would
also fix all other instances of this bug, if there are any.

Closes: #810622