Partial webform token replacement

I have a webform with a nested field structure, so I have a number of fieldsets and then textfields or whatever within them. Not all of the fields are mandatory.

Then when the form is submitted I'm using the following token to print the entered value for one of the optional textfields: %value[fieldset1][address2]

According to the code, all empty fields have their tokens replaced with an empty string, but what is actually happening in my case is that %value[fieldset1] gets replaced with an empty string and the [address2] is still appears in the email text.

This is because the replacement for %value[fieldset1] happens first. Really we should replace all children first, and then work our way up to the parents. The attached patch fixes the problem for me. It reverse sorts the email replacements array on its key, meaning longer keys are replaced first, and since a child will always have a longer key than its parent, I think this should work quite well.