Divide by zero bug in ercf.py code due to filament misfeed in filament block (Sensorless branch)

[nightime7]

Lines 409-411 in ercf.py include the below logic:

409 self._load_to_end_of_bowden(load_length-encoder_moved)
410 final_position = self._counter.get_distance()
411 ratio = load_length / final_position

if self_counter-get_distance() returns '0' due to misfeed of filament in cartrige, this will cause an internal error in klipper and shutdown the printer.
There should be applied a check for zero value in final_position prior to line 411.

[jwhite]

I got hit by this. Create a pull request?