StateAttribute: ClonedAttribute may overwrite original uniform

[Kuranes]

StateAttribute::apply may contain per attribute uniform,
and as TypeMember is the same between cloned and original, uniform cache will return the same uniform for both, and will then be overwritten if not handled with an early out return code

if (!this._enable)return ; 

(need to update example shader generator sample to advertize the possible behaviour)

[cedricpinson]

Should not be a problem, I added extra check in State.js with this PR #382 that would help to find the real problem.
We should not update code with

 if ( !this._enable) return;

instead find the real source of the problem