fix: don't call the retry prompt if a command has a default value

[Norviah]

issue

when executing Argument.process, choice is called to determine if the command has optional arguments or not. the problem being in the first parameter, this.prompt && this.prompt.optional, determines if a optional value is set within a command's args object, however it doesn't check if a default value is set.

so, if a command is ran with a default value, a retry prompt is still executed as the first parameter doesn't check if a default value is set for the argument.

example

if we have a command with args set as

// alias: greet
args: [
  {
    id: 'member',
    type: 'member',
    prompt: { retry: 'please provide a valid member.' },
    default: (message: Message) => message.member,
  },
],

and the command is run as .greet, a retry prompt is called even though the command has a default value set.

solution

the solution is rather simple, just check if the command has a default value before checking if the optional property is set within the command's prompt.