Fixed issue where multiple results files for a single feature causes exceptions when processing scenario outline examples.

A bit of an edge case here, but hey, this is how I'm using it!

I run NUnit with two passes. The first pass only runs tests from a "work in progress" category - this test run does not fail the build if any test fails. The second pass runs tests from all categories except for those that were run in the first pass - this test run does fail the build if any test fails. The two passes generate two NUnit results files for a single SpecFlow feature file.

When running Pickles against a single feature, but with two NUnit results files, I noticed that an exception was thrown when trying to parse test examples from Scenario Outlines.

The following commit should fix this problem. Try running the unit test without the changes in NUnitSingleResults.cs - the test should fail. Apply my changes and the test should pass.