don't use diagnosers when running the benchmark has failed

[adamsitnik]

Fixes few issues:

• when OverheadJitting succeeds, but workload fails there are some measurements reported. I've improved the check to take this into account:

- if (!measurements.Any())
+ if (!measurements.Any(measurement => measurement.IsWorkload()))

• when few iterations run OK, but then some fail the MemoryDiagnoser (which runs at the end) is not collecting any data, hence there is nothing to parse. I've changed lines.Last to lines.LastOrDefault to account for that

• when we know that the benchmarking has failed, we should not try to run any diagnosers

fixes #1803

cc @jeffhandley who has reported this bug offline