Fixed trsinc in Viscoelastic.f90 to avoid division by zero
Fixed trsinc in Viscoelastic.f90 to avoid division by zero

FrontISTR/FrontISTR,FrontISTR/FrontISTR,FrontISTR/FrontISTR,FrontISTR/FrontISTR,FrontISTR/FrontISTR