Fix -Wsign-conversion error by adding static_cast
Fix -Wsign-conversion error by adding static_cast

jlanecox/googletest,jlanecox/googletest,antidotcb/googletest,antidotcb/googletest,google/googletest,xnagireddy/googletest,jlanecox/googletest,empiredan/googletest,empiredan/googletest,antidotcb/googletest,google/googletest,xnagireddy/googletest,antidotcb/googletest,gianricardo/googletest,google/googletest,xnagireddy/googletest,google/googletest,gianricardo/googletest,empiredan/googletest,xnagireddy/googletest,jlanecox/googletest,gianricardo/googletest