simd_cast: add helper overload for offset > input
simd_cast: add helper overload for offset > input

If the requested offset to simd_cast_with_offset is larger than the
input just return Return::Zero(). This is easier to generalize than
adding the logic for avoiding this call altogether.

Signed-off-by: Matthias Kretz <372ea4eca737a13cd010ee806d4ce7b98ee71550@kde.org>

chr-engwer/Vc,chr-engwer/Vc,VcDevel/Vc,chr-engwer/Vc,VcDevel/Vc,VcDevel/Vc,VcDevel/Vc