[C++] test failure with zstd 1.3.7

[asfimport]

We may pass a NULL output pointer to Codec::Decompress when the output size is 0, but recent zstd versions don't like that.

This was already identified (and patched on the side) by one of our packagers:
NixOS/nixpkgs#48928

Reporter: Antoine Pitrou / @pitrou
Assignee: Antoine Pitrou / @pitrou

PRs and other links:

• GitHub Pull Request #2909

_{Note: This issue was originally created as ARROW-3707. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 2909
#2909