Handle empty chat output better

What does this MR do?

If the output was empty we would end up running ''.split("\n"),
producing an empty Array. Slicing an empty Array using a range such as
1..-1 would then produce a nil value, instead of an empty Array. This in turn would cause a NoMethodError since "join" is not defined for
NilClass.

Example:

[][1..-1] # => nil
['foo'][1..-1] # => []

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together