[SofaConstraint] Fix crash when constraint correction is missing

[alxbilger]

The LCPConstraintSolver in its unbuilt version crashed when a contact does not have an associated constraint correction, because of a null pointer dereference.

Now, the pointer is checked for null. Also, if there are only contacts without constraint correction, the algorithm stops.

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Reviewers will merge this pull-request only if

• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
• it does not generate new unit test failures.
• it does not generate new scene test failures.
• it does not break API compatibility.
• it is more than 1 week old (or has fast-merge label).

[fredroy]

[ci-build][with-all-tests]