generate the old key before updating enabledborders

Summary:
sometimes a frame changed enabled borders causing a dangling
pointer in s_sharedFrames, since oldkey was generated
with the new enabled borders, it generated a key not present
in the hash, tryed to remove it and left the one associated
with the old key in the hash.
if the need to reuse a frame with that key ever arised again,
we had a crash
BUG:378508

Test Plan:
couldn't reproduce the crash neither with or without patch,
with the patch, if i put debug in every place a framedata is removed,
searching if the key is in the hash before removing it, now
it's always true, before sometimes it was false

Reviewers: Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: plasma-devel, Frameworks

Tags: Plasma, Frameworks

Differential Revision: https://phabricator.kde.org/D6162