Fix for cascading mailer path being added to template path when using…

… partials in email templates

As per padrino#2231, when using multiple partials within an email template, the mailer name keeps getting added to the file path for each subsequent partial in the same template, resulting in an `Errno::ENOENT: No such file or directory @ rb_sysopen` error.

Added a check to `settings.view` in the render routine to see if the mailer path was already in the string before adding it.

padrino-mailer/lib/padrino-mailer/ext.rb

@@ -261,7 +261,7 @@ def render(engine=nil, data=nil, options={}, locals={}, &block)
       engine ||= message_name
 
       if mailer_name && !engine.to_s.index('/')
-        settings.views += "/#{mailer_name}" 
+        settings.views += "/#{mailer_name}" unless settings.views.include?("/#{mailer_name}")
         engine = engine.to_s.sub(%r{^#{mailer_name}/}, '')
       end