LCMS: fix value range detection of YCbCr profiles

Wolthera's right, YCbCr (when used full-range, ICC doesn't allow
otherwise) is a reinterpretation of RGB. However, my profiles implement
roundtrip transformation through the AtoB0 and BtoA0 (plus the FP
alternatives) so returning early breaks the purpose of having them.

This commit moves the clause to the correct location and lets the
roundtrip check execute first.

CCMAIL: kimageshop@kde.org