MadGraphControl: fix on-the-fly dictionary tweak for Python3
Couple more instances of dictionaries being modified while looping over them, which needs a bit of TLC in Python3.
Fix by making a genuine clone of the list.
cc @ewelina
Couple more instances of dictionaries being modified while looping over them, which needs a bit of TLC in Python3.
Fix by making a genuine clone of the list.
cc @ewelina