[SIMD] fix Solvers - if one lane has zero initial residual

Nils-Arne Dreierrequested to merge
fix_cgsolver_simd_zero_residual into master

If one lane has zero residual (e.g. the RHS and initial guess is zero) the division in the factor for the minimizing and orthogonalization is handled explicitly to avoid NaNs.

Edited by Nils-Arne Dreier

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