The Prepare method of TPyLocalEnvironment allows invalid Distributions

[peardox]

The JSON file provided as FilePath may contain invalid entries that don't point to files and directories on the target system.

When processing the individual entries Prepare's Anonymous method should verify the existance of the files and directories before adding the Distribution.

It is also possible to add the same entry multiple times resulting in more than one valid entry for a Distribution

[lmbelo]

Distributions can be set statically. The environment where it was set might not contain the same settings as the target environment. We can't validate it on setting up step. However, we can validate it as we try to activate the environment.