Fix maybe-uninitialized warnings in WorkItemBuiltins
Fix maybe-uninitialized warnings in WorkItemBuiltins

surround-io/oclgrind,mpflanzer/Oclgrind,mpflanzer/Oclgrind,surround-io/oclgrind,surround-io/oclgrind,surround-io/oclgrind,mpflanzer/Oclgrind,mpflanzer/Oclgrind