Fixed that MailHandler#plain_text_body was returning nil if there was nothing to strip (#2814).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@2520 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/mail_handler.rb

@@ -235,6 +235,7 @@ class MailHandler < ActionMailer::Base
       @plain_text_body = plain_text_part.body.to_s
     end
     @plain_text_body.strip!
+    @plain_text_body
   end