FIX: An error would be raised if fewer than "skip_messages" existed

lib/discourse_chat/provider/slack/slack_transcript.rb

@@ -34,6 +34,7 @@ module DiscourseChat::Provider::SlackProvider
     # Apply a heuristic to decide which is the first message in the current conversation
     def guess_first_message(skip_messages: 5) # Can skip the last n messages
       return true if @requested_thread_ts # Always start thread on first message
+      return false if @messages.blank? || @messages.size < skip_messages
 
       possible_first_messages = @messages[0..-skip_messages]
 

spec/lib/discourse_chat/provider/slack/slack_transcript_spec.rb

@@ -96,6 +96,11 @@ RSpec.describe DiscourseChat::Provider::SlackProvider::SlackTranscript do
     SiteSetting.chat_integration_slack_access_token = "abcde"
   end
 
+  it "doesn't raise an error when there are no messages to guess" do
+    transcript.instance_variable_set(:@messages, [])
+    expect(transcript.guess_first_message(skip_messages: 1)).to eq(false)
+  end
+
   describe 'loading users' do
     it 'loads users correctly' do
       stub_request(:post, "https://slack.com/api/users.list")