For #26218 - Fixed various initialisation issues.

Found and fixed a few edge cases that would throw 'PythonObject is not attached to a node' errors in Nuke, resulting in the app not being loaded and the script being left in an error'd state.
This feels unclear. Is this structure a list which is supposed to change its size over time (hence a list rather than a tuple?) In case it is supposed to only contain two boolean values, is it clearer to just have to member variables?