[2.6] Don't send extruder stack to CuraEngine when there is only 1 extruder

[fieldOfView]

This PR fixes an issue which causes settings to be ignored if a Custom FDM Printer is used with the number of extruders set to 1. Fixes #2007

When there is 1 extruder, the frontend stores all settings in the global stack. Sending an extruder stack confuses CuraEngine into using the values of the extruder stack, which results in defaults being used.

Basically, single extrusion Custom FDM Printers are broken at the moment, so if there were a point-release for Cura 2.6 it would be great if this fix could be included.

Steps to reproduce:

• Add a Custom FDM Printer
• Keep number of extruders to 1, keep diameter at 2.85
• Slice an object, and note down the estimated length of material.
• Change the diameter to 1.75 in the sidebar
• Note that after slicing the estimated length has changed
• Save the gcode file, and inspect the last G1 before the end gcode

Expected:
The E-value for the last G1 reflects the changed amount of material

Actual:
The E-value for the last G1 reflects the original amount of material, for 2.85 mm diameter.

[nallath]

Thanks for the fast fix!

[BagelOrb]

The problem seems fixed, but when I create a new Custon FDM Printer, the default material diameter is set to 1.75. Changing it to 2.85 doesn't have any effect on the material diameter in the side panel.

It seems to me that the material diameter should be removed from the machine settings...

If I change the side-panel value, the machine setting changes along, but not the other way around.

[fieldOfView]

It seems to me that the material diameter should be removed from the machine settings...

We need a way to set the filament diameter the printer requires.

the default material diameter is set to 1.75. Changing it to 2.85 doesn't have any effect on the material diameter in the side panel.

Hmm, the problem is that the diameter gets overridden by the currently active material... Something to fix in Cura 2.7