opts: fix potential integer overflow CWE-190, CWE-681
opts: fix potential integer overflow CWE-190, CWE-681

Caught by CodeQL:

> Incorrect conversion of an integer with architecture-dependent bit size
> from strconv.ParseUint to a lower bit size type uint16 without an upper
> bound check.

fixes https://github.com/docker/cli/security/code-scanning/2

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

cpuguy83/cli,thaJeztah/cli,docker/cli,cpuguy83/cli,thaJeztah/cli,docker/cli