Slice error with multi-filament interlocking, with boundary avoidence = 0

[Noisyfox]

Application Version
5.7.2

Platform
N/A

Qt
N/A

PyQt
N/A

Display Driver
N/A

Steps to Reproduce

1. Add two objects that overlaps each other
2. Apply different extruders
3. Enable interlocking, with boundary avoidence = 0
4. Make sure the bottom surface has two adjacent colors
5. Slice

Actual Results
Slice failed

Expected results
Slice properly

Additional Information

[Noisyfox]

When boundary avoidence set to 0, voxels below z=0 won't be removed, which caused this error.

[Noisyfox]

One quick solution is to change

CuraEngine/src/InterlockingGenerator.cpp

Lines 203 to 207 in 2f395b0

	auto voxel_emplacer = [&cells](GridPoint3 p)
	{
	cells.emplace(p);
	return true;
	};

to

    auto voxel_emplacer = [&cells](GridPoint3 p)
    {
        if (p.z_< 0) return true;

        cells.emplace(p);
        return true;
    };