[Buglet] "git show <random-40-hexdigit>" gives an unclear error message

Here is one who wants to tackle potentially a low-hanging fruit.

  $ git cat-file -p 4cd96ce446ab653325a0e47fad73e94c99c57dd2
  error: unable to find 4cd96ce446ab653325a0e47fad73e94c99c57dd2
  fatal: Not a valid object name 4cd96ce446ab653325a0e47fad73e94c99c57dd2

This looks sensible and understandable, even though you could argue that we don't have to say the same thing twice. In the same repository:

  $ git show 4cd96ce446ab653325a0e47fad73e94c99c57dd3
  fatal: bad object 4cd96ce446ab653325a0e47fad73e94c99c57dd3

This is bad, as it sounds as if we found the named object but it is corrupt.