Bug#325009: Error handling bugs

[Ian Jackson <ian@davenant.greenend.org.uk>]

Package: apt
Version: 0.6.40.1

There are places in apt where it calls a function like FileFd::Open
but fails to check the boolean success/failure value.

Even in cases where this does not cause undefined behaviour it can
cause strange and confusing error messages as, after the first call
has failed and reported its failure, the code blunders on printing a
bunch of consequential errors.

For example,
 in apt-get.cc, DoCheck
 in indexcopy.cc, SigVerify::CopyMetaIndex and other places

All other code in apt written by the authors of these mistakes should
be thoroughly inspected (by eye or mechanically somehow) for similar
problems - for example, by trying to get a compiler to report all
places where a `boolean' return value is ignored.

This bug report should not be closed until that inspection and
resulting remedies are complete.  Any other remedy will mean piecemeal
finding and fixing of these kind of bugs for years to come.

Thanks,
Ian.