Merge "follows the advice of -Wsign-compare" am: 1545889256 am: c1c27d597c am: 361384c81d

Original change: https://android-review.googlesource.com/c/platform/system/tools/sysprop/+/1613110

Change-Id: I0be2a7b3a2d43f86fb54cd1b07446ce66fe1cfc2