Adjust fix_display() to work when tkinter is not installed

[musicinmybrain]

This handles the case where tkinter is None because it isn’t installed, e.g. on Fedora, the python3-tkinter subpackage is not installed.

sciunit/sciunit/base.py

Lines 17 to 20 in 1a2ca47

	try:
	import tkinter
	except ImportError:
	tkinter = None