Protect the ScriptRepository from empty string

the Algorithm UpdateScriptRepository first check if the repository is valid,
meaning, it is installed and correct.

Protect ScriptRepositoryImpl from empty ScriptRepositoryLocal string.

re #6923
Do not trigger UpdateScriptRepository if it is not installed

if the user never installed the ScriptRepository, it should not try to
update it. As so now.

re #6923
Correct the bug found for the installation of ScriptRepository

Ubuntu used to define non initialized bool attribute as false, but, windows
does seems to initialize them as true. So, the error presented by the test:

{{{
ScriptRepository: Corrupted database : .repository.json
}}}

was not seem at my development environment (ubuntu). This commit does
initialize the valid attribute to fix this issue.

re #6923
Addition of a unit test that reproduce the error found

This is to protect for future erros like this.

The error is that the remote url is empty.

re #6923
Protection from empty remote url

Correct the steps of construction, first get the remote url information,
and them the local paths. Besides, protect install method to attempt
to install on an empty remote_url.

re #6923
Merge remote-tracking branch 'origin/bugfix/6923_auto_update'