[Path] Fix open edge zero value start point

[Russ4262]

forum mention at https://forum.freecadweb.org/viewtopic.php?f=15&t=64882
This fix applies a small value to start points for open edges when either the x or y start point value is roughly zero.

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[freecadci]

for feature branch PR_5343. Pipeline 443190374 was triggered at 9c83410. All CI branches and pipelines.

[benj5378]

The code looks fine. I haven't tested the functionality

[agren]

I might be mistaken but I'm not sure this is a bug in Path.fromShapes().
If you do a Path.show(pp, "pp") after line 290. You can see that fromShapes() return same shaped paths irregardless of the value of x.

If the bug was in fromShapes i would expect fromShapes to return different-shaped paths when x=0 and x=1

[agren]

Adding an image that hopefully clarifies what I try to say.

[Russ4262]

I grabbed a recent weekly build:
OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.20.27428 (Git)
Build type: Release
Branch: master
Hash: 2746035
Python version: 3.8.6+
Qt version: 5.15.2
Coin version: 4.0.1
OCC version: 7.5.3
Locale: English/United States (en_US)

... and this is the result with what appears to be the same test file as you present above in the image.

Applying the proposed fix in this PR corrects the path generated, as seen in the following image, and is applied in the following FreeCAD version:
OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.20.27496 +2 (Git)
Build type: Release
Branch: fix/3D_pocket_overcut
Hash: f1a223e
Python version: 3.8.6+
Qt version: 5.15.2
Coin version: 4.0.1
OCC version: 7.5.3
Locale: English/United States (en_US)

I have not looked at code for Path.fromShapes() to determine if a bug exists there. As presented in the original test file by Lupin in the forum, the zero passed in the pathParams["start"] vector parameter are causing, or related to, the problem. This PR intervenes within the python to make those zeros a very small non-zero number, which seems to correct the issue within the gcode output.

Thanks for reviewing and collaborating on this bug.

Russell

[agren]

Sorry, I could have been clearer. I was not doubting your fix, it works. I was only doubting that the bug is in fromShapes. But I'm not so sure anymore.

Looking closer at the output generated by fromShapes does indeed show that the x feed is omitted when the X=0 in the start param.
Rapids between layers with model x=0:

Command G0 [ Z:5 ],
Command G0 [ Y:13 ],
Command G0 [ Z:3 ]

Rapids between layers with model x=1:

Command G0 [ Z:5 ],
Command G0 [ X:1 Y:13 ],
Command G0 [ Z:3 ]

So long story short. Ignore what I said :)

[freecadci]

for feature branch PR_5343. Pipeline 470441361 was triggered at 9227b4a. All CI branches and pipelines.