[C++] Segfault when comparing status with and without detail #23973

I noticed this while working on Flight integration tests. The equality operator for Status doesn't check whether the status detail is nullptr before dereferencing it.

Reporter: David Li / @lidavidm
Assignee: David Li / @lidavidm

PRs and other links:

• GitHub Pull Request #6332

_{Note: This issue was originally created as ARROW-7734. Please see the migration documentation for further details.}