Bug fixed: On some environment the maximum value from mt_rand() is less than 12 figures so you need to check the maximum. props oivindmo on http://wordpress.org/support/topic/bug-when-sending-file

git-svn-id: https://plugins.svn.wordpress.org/contact-form-7/trunk@977085 b8457f37-d9ea-0310-8a92-e5e31aec5664