Fix build of adb with gcc-4.9.

Without this patch we get:

system/core/adb/commandline.c:1629:16: error: array subscript is above
array bounds [-Werror=array-bounds]

Change-Id: I494eb8b4d0e8082f8ff57bdd33d8d46c8c481c6f
Signed-off-by: Alexander Ivchenko <alexander.ivchenko@intel.com>