ext_poisson does not build

[sven-ds]

Checklist

• I have searched for similar issues.
• For Python issues, I have tested with the latest development wheel.
• I have checked the release documentation and the latest documentation (for master branch).

Describe the issue

In version 0.17.0, ext_poisson does not build because Werror=maybe_uninitialized and the compiler found that some variables may be uninitialized

Steps to reproduce the bug

followed http://www.open3d.org/docs/release/compilation.html

Error message

/home/sven/git/Open3D/build/poisson/src/ext_poisson/PoissonRecon/Src/RegularTree.inl:251:36: error: ‘c’ may be used uninitialized [-Werror=maybe-uninitialized]
251 | if( !i || d>c ) c=d;

/home/sven/git/Open3D/build/poisson/src/ext_poisson/PoissonRecon/Src/RegularTree.inl: In function ‘int RegularTreeNode<Dim, NodeData, DepthAndOffsetType>::maxDepth() const [with unsigned int Dim = 3; NodeData = FEMTreeNodeData; DepthAndOffsetType = short unsigned int]’:
/home/sven/git/Open3D/build/poisson/src/ext_poisson/PoissonRecon/Src/RegularTree.inl:247:21: note: ‘c’ was declared here
247 | int c , d;

/home/sven/git/Open3D/build/poisson/src/ext_poisson/PoissonRecon/Src/FEMTree.IsoSurface.specialized.inl:1562:37: error: ‘start’ may be used uninitialized [-Werror=maybe-uninitialized]
1562 | position[o] = Real( start + width*averageRoot );

/home/sven/git/Open3D/build/poisson/src/ext_poisson/PoissonRecon/Src/FEMTree.IsoSurface.specialized.inl: In lambda function:
/home/sven/git/Open3D/build/poisson/src/ext_poisson/PoissonRecon/Src/FEMTree.IsoSurface.specialized.inl:1511:22: note: ‘start’ was declared here
1511 | Real start , width;

Expected behavior

everything compiles without warning or -Werror is not set :)

Open3D, Python and System information

- Operating system: Ubuntu 23.04 
- Python version: 3.11.2 (main, Mar 13 2023, 12:18:29) [GCC 12.2.0]
- Open3D version: output from python: v0.17.0
- System architecture: x86 
- Is this a remote workstation?: no
- How did you install Open3D?: build from source
- Compiler version (if built from source): gcc (Ubuntu 12.2.0-17ubuntu1) 12.2.0

Additional information

No response

[riccardorosalen]

Having the same isssue, I'm using Ubuntu 23.04

[Balisa16]

I also have same issue.

1. Open3D/build/poisson/src/ext_poisson/PoissonRecon/Src/RegularTree.inl:251:36: error: ‘c’ may be used uninitialized
2. Open3D/build/poisson/src/ext_poisson/PoissonRecon/Src/FEMTree.IsoSurface.specialized.inl:1562:37: error: ‘start’ may be used uninitialized [-Werror=maybe-uninitialized]

I fixed it with just adding "0" init value.

and

[sitic]

PR #6039 fixes this issue