This construct "current_x = x or current_x" was not correctly handling
cases where x could be 0 and current_x None, and current_x still be None
after the statement while it should have been 0.

Conflicts:
	printrun/printcore.py
	printrun/printrun_utils.py

This reverts commit 1877d2cc.

Conflicts:
	printrun/gcoder.py