Single form multiple submit
You can try out a more general solution for all the forms by using Hide Submit Module


  Some users accidentally click the submit button more than once while
  waiting for their post to be saved. In some cases this may result
  duplicate postings or duplicate e-commerce orders.
  
  There are few ideas on how to solve duplicate postings but none is
  perfect. One of the solutions is a bit of jQuery to hide or disable
  the submit button after it has been clicked and replace it with an
  informative text such as "Processing..." .
  
  This module wraps that jQuery code and provides some options. Of
  course this, too, is not a perfect solution as it requires Javascript
  to be enabled. For browsers with Javascript disabled this module will
  have no effect at all.