fix a bug of WeakformPrcessor that let setEnableMultiThread() be unfunctional
fix a bug in WeakformProcessor.prepareProcessNodesDatas()
trivial code format for some lines
let Model2D accept null polygon
let WeakformProcessor adopt null constitutiveLaw and model polygon
accelerate two VisibleSupportDomainSearchers when no segments lay in support domain
add MLSLevelSetDemo