Fixes blank page error

Fix to avoid blank page error, apparently prevents a memory exausted condition.

Error source: 
http://wordpress.org/support/topic/blank-page-after-return-form-cielo-buypage?replies=15

Some info:
http://stackoverflow.com/questions/8379829/domdocument-php-memory-leak

Another people using the same code: http://nathanstaines.com/articles/wordpress-word-count/

Cheers,
Gabriel
Merge pull request #3783 from greguly/patch-1

Fixes blank page error