A slight change for stability

While updating ie_cgenericelement_uaf earlier today, I noticed the changes made it a tiny bit less stable. Juan's test log in #1809 also kinda shows that (with the first attempt failing), so I decided to go back and move the string crafting part, that way between CollectGarbage() and the overwrite, there is less noise, and hopefully more stable.  I did a few tests, seems better.