[Feature Request] Validate inject_code path before trying to inject to a service

[fidel]

Is your feature request related to a problem? Please describe.
It could avoid problems if we would check if the path to an inject_file is valid before injecting it.

Describe the solution you'd like
check if path is valid / file exists

Describe alternatives you've considered

• Dont try to inject it if path isnt valid
• Report warning to user

Additional context
Might be related with #184

[fidel]

Question:
the relative inject code path in the serviceList is using linux path notation.
Is that properly handled on i.e. Windows Machines?