fix: send a proper empty response when populating autocomplete with no choices

[V3ntus]

About

Instead of sending an empty list, which Discord will not accept, send an empty field for choices

...
	await ctx.populate(choices=[])
	# or
	await ctx.populate(choices=None)
	# will now result in Discord sending "No options match your search"
	# instead of "Loading options failed" previously

Checklist

• I've ran pre-commit to format and lint the change(s) made.
• I've checked to make sure the change(s) work on 3.8.6 and higher.
• This fixes/solves an Issue.
  • (If existent): [BUG] ctx.populate for autocomplete does not send proper empty data #755
• I've made this pull request for/as: (check all that apply)
  • Documentation
  • Breaking change
  • New feature/enhancement
  • Bugfix