Blender Git Loki

Fix T56498: Segment fault when change parameter of one operator after undo.

You cannot store ID (or any other data) pointers accross undo?s/redo?s, those
are reading .blend file and hence invalidating all pointers!

Not that happy with this fix, code is rather convoluted and not elegant
at all, but cannot think of a better solution, so will do for now.

Also found and fixed another 'str ghash used for int keys' case...