ethdebug: correct handling of abstract contracts.

[aarlt]

No description provided.

[cameel]

You should do this to get saner diff :)

Suggested change

	if (_linkerObject)
	{
	if (!_linkerObject)
	Json::array();

[cameel]

But also why is it even called when the object is null? Wouldn't make more sense to just skip it?

[ekpyron]

For the record: I'm approving this PR and setting it to merge, even though this is a mild violation of the ethdebug spec - we shouldn't produce "program" ethdebug output for anything that doesn't produce any actual bytecode - so ideally we should already filter out abstract contracts and interfaces earlier than here - which would likely mean both in CommandLineInterface and in StandardCompiler (in the latter case we should make it an error, if ethdebug program output is specifically requested for an interface/abstract contract, while just skipping them for a wildcard request).

But the PR fixes the actual usage limitation here (which would have been a bit unfortunate to have kept in for the release), and there's no harm in producing this output, so we can keep it as is and adjust this properly after the release.