fix: allow debugging inside __init__.robot files

[Blashaq]

RobotFramework allows to specify folder-wide initialization file __init__robot. Sadly listener API does not pass this file to the start_keyword listener method- instead giving only directory path. This causes RF-debuglibrary to crash inside __init__.robot files.

This PR fixes this by checking if the path is actually a file- if not, verify if there is indeed an __init__ file in this directory. If it is the case, assume that we are inside this file.