NoMethodError when listing a file that contains periods only

[TheLastZombie]

Description

When running colorls -a or colorls -A inside a directory that contains a file whose name consists solely of dots, an error is thrown:

Traceback (most recent call last):
	16: from /usr/local/bin/colorls:23:in `<main>'
	15: from /usr/local/bin/colorls:23:in `load'
	14: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/exe/colorls:26:in `<top (required)>'
	13: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/flags.rb:32:in `process'
	12: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/flags.rb:32:in `each_with_index'
	11: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/flags.rb:32:in `each'
	10: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/flags.rb:41:in `block in process'
	 9: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/core.rb:55:in `ls'
	 8: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/layout.rb:14:in `each_line'
	 7: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/layout.rb:14:in `each'
	 6: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/layout.rb:14:in `block in each_line'
	 5: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/core.rb:56:in `block in ls'
	 4: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/core.rb:322:in `ls_line'
	 3: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/core.rb:322:in `each_with_index'
	 2: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/core.rb:322:in `each'
	 1: from /var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/core.rb:323:in `block in ls_line'
/var/lib/gems/2.7.0/gems/colorls-1.4.3/lib/colorls/core.rb:350:in `options': undefined method `downcase' for nil:NilClass (NoMethodError)

To reproduce: touch ... && colorls -a

---

• Relevant Issues : (none)
• Relevant PRs : (none)
• Type of issue :
  • Installation
  • Font-related
  • Feature request
  • Bug in existing feature
  • Developer mode : Code quality / Tests / Documentation