Merge branch 'tr/fd-gotcha-fixes'

Two places we did not check return value (expected to be a file
descriptor) correctly.

* tr/fd-gotcha-fixes:
  run-command: dup_devnull(): guard against syscalls failing
  git_mkstemps: correctly test return value of open()

diff --cc run-command.c
Simple merge

diff --cc wrapper.c
Simple merge