Fixes help querying

- If a non-existent command with a flag is queried to Cask, the latter
is printed instead of the command
 - If the help from a not-yet-tapped cask's command is queried, it
prints brew tap's help infinitely

Fixes caskroom/homebrew-cask#28977

Library/Homebrew/brew.rb

@@ -32,7 +32,7 @@ begin
 
   empty_argv = ARGV.empty?
   help_flag_list = %w[-h --help --usage -?]
-  help_flag = !ENV["HOMEBREW_HELP"].nil?
+  help_flag = false
   internal_cmd = true
   cmd = nil
 
@@ -44,6 +44,9 @@ begin
       help_flag = true
     elsif !cmd && !help_flag_list.include?(arg)
       cmd = ARGV.delete_at(i)
+    elsif help_flag_list.include?(arg) & cmd
+      # cmd determined, and it needs help
+      help_flag = true
     end
   end
 

Library/Homebrew/cask/lib/hbc/cli.rb

@@ -231,7 +231,7 @@ module Hbc
         return if @command == "help" && @args.empty?
 
         unknown_command = @args.empty? ? @command : @args.first
-        raise ArgumentError, "Unknown command: #{unknown_command}"
+        raise ArgumentError, "Unknown command: #{@command} #{@args.join(" ")}"
       end
 
       def purpose