Quick fix in update fine search candidate for map accessors

[acdaigneault]

Description of the problem

• Weird crashes (segfault) in the update_fine_search_candidates() function related to the particle-particle containers
• Seems related to load balancing or the contact threshold or neither of that
• We still do not understand why the changes fixed the crashes and we are not sure it will prevent other crashes or it just fixed our edge case.
• Our hypothesis right now should be that the issues came from the way the particle contact data structure was not being cleared correctly after load balancing or particle location/distribution.

Description of the solution

• Change accessor from [] to .find() for the candidate containers (broad search)

How Has This Been Tested?

• Tests are good

[blaisb]

@OGaboriault Tell me when you think this is ready for merge I think this is good, so most likely I will merge it tomorrow or smthing

[acdaigneault]

I change a few [] in the broad search also