bslstl_charconv.t.cpp: prevent undefined behavior on LLONG_MIN (#3014)
bslstl_charconv.t.cpp: prevent undefined behavior on LLONG_MIN (#3014)

* bslstl_charconv.t.cpp: prevent undefined behavior on LLONG_MIN

* bslstl_charconv.t.cpp: fixed another problem

bloomberg/bde,bloomberg/bde,bloomberg/bde,bloomberg/bde,bloomberg/bde