Add test to validate empty patch

[uilianries]

Description of your Pull Request

The issue #35 brings the case when an empty patch is tried to be applied, it fails in the end.

This is a scenario when doing chmod or similar only to a file, where no line is changed in the end. As a result, patch-ng can not understand it as it parser looks for the index @@ -0,0 +1 @@ (and similar).

This PR provides a test to validate that case, but does not bring a solution, because it will affect not only the patch parse logic profoundly, but also its regex. I'm afraid is too risky trying to fix it, but without breaking something else later, as this fork is supposed to be more conservative.

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• If the issue has missing info, explain the purpose/use case/pain/need that covers this Pull Request.
• I've tested locally that my code works.
• I've added relevant tests to verify that my code works.