Fix style reset in job log

When ANSI sequence is empty (\e[m) issue a
style reset, same as \e[0m

changelogs/unreleased/fix-job-log-style-reset.yml

+---
+title: Fix style reset in job log when empty ANSI sequence is encoutered
+merge_request: 20367
+author:
+type: fixed

lib/gitlab/ci/ansi2json/style.rb

@@ -15,14 +15,10 @@ module Gitlab
         end
 
         def update(ansi_commands)
-          command = ansi_commands.shift
-          return unless command
-
-          if changes = Gitlab::Ci::Ansi2json::Parser.new(command, ansi_commands).changes
-            apply_changes(changes)
-          end
+          # treat e\[m as \e[0m
+          ansi_commands = ['0'] if ansi_commands.empty?
 
-          update(ansi_commands)
+          evaluate_stack_command(ansi_commands)
         end
 
         def set?
@@ -50,6 +46,17 @@ module Gitlab
 
         private
 
+        def evaluate_stack_command(ansi_commands)
+          command = ansi_commands.shift
+          return unless command
+
+          if changes = Gitlab::Ci::Ansi2json::Parser.new(command, ansi_commands).changes
+            apply_changes(changes)
+          end
+
+          evaluate_stack_command(ansi_commands)
+        end
+
         def apply_changes(changes)
           case
           when changes[:reset]

spec/lib/gitlab/ci/ansi2json/style_spec.rb

@@ -143,6 +143,7 @@ describe Gitlab::Ci::Ansi2json::Style do
         [[], %w[106], 'term-bg-l-cyan', 'sets bg color light cyan'],
         [[], %w[107], 'term-bg-l-white', 'sets bg color light white'],
         # reset
+        [%w[1], %w[], '', 'resets style from format bold'],
         [%w[1], %w[0], '', 'resets style from format bold'],
         [%w[1 3], %w[0], '', 'resets style from format bold and italic'],
         [%w[1 3 term-fg-l-red term-bg-yellow], %w[0], '', 'resets all formats and colors'],