If we have a rotate axis whose length is extremely large, we will get an
infinite value, and its normalized vector is a zero vector, instead of an
unit vector, i.e. (x/inf, y/inf, z/inf) == (0, 0, 0).
The solution is: we scale the vector, so the length becomes a finite value,
and we could get a valid unit vector. Therefore, we use
a different normalization method, robust_normalize().
MozReview-Commit-ID: L8SteFe09aO
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extra : rebase_source : 4568c8bf906a9246e4ef13672a9ed541852b974a
Boris Chiou