tidy/bins: fix false positive on non checked-in binary
tidy/bins: fix false positive on non checked-in binary

`git ls-files` now exits zero when called with a missing file; check
that the file is included in the output before reporting a checked-in
binary. Observed with git 2.10.1 and tripped by a symlink created by
tests:

src/test/run-make/issue-26006/out/time/deps/liblibc.rlib -> out/libc/liblibc.rlib

graydon/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,graydon/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust