cli: fix default flags when their command equivalents are disabled

[ttytm]

Fixes default flags not working as expected when their commands are disabled.

Example:

// foo.v
import cli { Command, CommandFlag }
import os

fn main() {
	mut cmd := Command{
		name: 'foo'
		version: '0.1.0'
		posix_mode: true
		defaults: struct {
			version: CommandFlag{false, true}
			help: CommandFlag{false, true}
		}
	}
	cmd.parse(os.args)
}

Current:

❯ v run foo.v --version
# no output

Updated:

❯ v run foo.v --version
foo version 0.1.0

[ttytm]

The fix is based on the other default commands execute functions

v/vlib/cli/help.v

Line 30 in 2e9b4cf

pub fn print_help_for_command(help_cmd Command) ! {

[spytheman]

Excellent work.