BUG: EditBox: Ensure state variable are initialized before calling "create()"

This commit fixes regression introduced by r23636.

The following tests are now passing:
 * py_StandaloneEditorWidgetTest
 * py_ThresholdThreadingTest
 * py_NeurosurgicalPlanningTutorialMarkupsSelfTest

The associated error was:

Traceback (most recent call last):
  File "/path/to/Slicer-build/lib/Slicer-4.3/qt-scripted-modules/Editor.py", line 244, in setup
    self.createEditBox()
  File "/path/to/Slicer-build/lib/Slicer-4.3/qt-scripted-modules/Editor.py", line 280, in createEditBox
    self.toolsBox = EditorLib.EditBox(self.editBoxFrame, optionsFrame=self.effectOptionsFrame)
  File "/path/to/Slicer-build/lib/Slicer-4.3/qt-scripted-modules/EditorLib/EditBox.py", line 74, in __init__
    self.create()
  File "/path/to/Slicer-build/lib/Slicer-4.3/qt-scripted-modules/EditorLib/EditBox.py", line 289, in create
    self._onParameterNodeModified(self.editUtil.getParameterNode())
  File "/path/to/Slicer-build/lib/Slicer-4.3/qt-scripted-modules/EditorLib/EditBox.py", line 105, in _onParameterNodeModified
    self._onEffectChanged(caller.GetParameter("effect"))
  File "/path/to/Slicer-build/lib/Slicer-4.3/qt-scripted-modules/EditorLib/EditBox.py", line 336, in _onEffectChanged
    if self.currentOption:
AttributeError: 'EditBox' object has no attribute 'currentOption'

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23639 3bd1e089-480b-0410-8dfb-8563597acbee