Keep header when setting added to empty section

(MODULES-1821) When adding a setting to an empty, pre-existing
section (one with just a [section] header), the header wasn't
written out.  This commit is meant to fix that problem.

lib/puppet/util/ini_file.rb

@@ -148,8 +148,8 @@ def save
             fh.puts("#{@section_prefix}#{section.name}#{@section_suffix}")
           end
 
-          if !section.new_section? && !section.empty?
-            # write all of the pre-existing settings
+          if !section.new_section?
+            # write all of the pre-existing lines
             (section.start_line..section.end_line).each do |line_num|
               line = lines[line_num]