Blender Git Loki

Fix T68499: weight paint gradient is broken with generative modifiers

Caused by rBac442da4a14d.

Above commit tweaked the logic to not only early out, but also set the
WPGradient_vertStore screen coord to FLT_MAX in case this original index
was visited before [gradientVertInit__mapFunc].
For generative modifiers though, we might get here multiple times for the
same orig index, resulting in a valid orig index being made invalid for
gradientVertUpdate__mapFunc [which would early out in case of FLT_MAX].

Restored original logic, so that setting FLT_MAX only really happens
when it should: when ED_view3d_project_float_object fails...

Maniphest Tasks: T68499

Differential Revision: https://developer.blender.org/D6282