Merge branch 'js/realpath-pathdup-fix'

Git v2.12 was shipped with an embarrassing breakage where various operations that verify paths given from the user stopped dying when seeing an issue, and instead later triggering segfault. * js/realpath-pathdup-fix: real_pathdup(): fix callsites that wanted it to die on error t1501: demonstrate NULL pointer access with invalid GIT_WORK_TREE