setup: fix windows path buffer over-stepping

Fix a buffer over-stepping issue triggered by providing an absolute path that is similar to the work tree path. abspath_part_inside_repo() may currently increment the path pointer by offset_1st_component() + wtlen, which is too much, since offset_1st_component() is a subset of wtlen. For the *nix-style prefix '/', this does (by luck) not cause any issues, since offset_1st_component() is 1 and there will always be a '/' or '\0' that can "absorb" this. In the case of DOS-style prefixes though, the offset_1st_component() is 3 and this can potentially over-step the string buffer. For example if work_tree = "c:/r" path = "c:/rl" Then wtlen is 4, and incrementing the path pointer by (3 + 4) would end up 2 bytes outside a string buffer of length 6. Similarly if work_tree = "c:/r" path = "c:/rl/d/a" Then (since the loop starts by also incrementing the pointer one step), this would mean that the function would miss checking if "c:/rl/d" could be the work_tree, arguably this is unlikely though, since it would only be possible with symlinks on windows. Fix this by simply avoiding to increment by offset_1st_component() and wtlen at the same time. Signed-off-by: Martin Erik Werner <martinerikwerner@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>