Debug ci fix

[blaisb]

Description

There were some asserts being thrown in debug mode. These asserts were all warrented.
They were cuased by the following:
1- std::shared_ptr cannot be created from a nullptr. Since the sharp edge in the tracer relies on this mechanism to assess if there is or not a shape, this was highly problematic. @oguevremont we will need to look more into this and refactor this more cleanly in the next month. I have made a solution using regular pointers which is fine, but relying on nullptr is not very nice in my opinion
2- There was an std::vector that was not used correctly in the find cell around flat mechanism
3- In the restart for sharp edge, the order of the checks was not done in the right order which violated the size issue.

Solution

Fixed all of those bugs.

Testing

Debug tests should pass now.

Code related list:

• All in-code documentation related to this PR is up to date (Doxygen format)
• Lethe documentation is up to date
• Fix has unit test(s) (preferred) or application test(s), and restart files are in the generator folder
• The branch is rebased onto master
• Changelog (CHANGELOG.md) is up to date
• Code is indented with indent-all and .prm files (examples and tests) with prm-indent

Pull request related list:

• Labels are applied
• There are at least 2 reviewers (or 1 if small feature) excluding the responsible for the merge
• If this PR closes an issue or is related to a project, it is linked in the "Projects" or "Development" section
• If the fix is temporary, an issue is opened
• The PR description is cleaned and ready for merge