Assert in 3d viewer with rounded rectangle pad with 50% radius

Steps:

* Make a footprint with a pad with a rounded rectangle with 50% radius
* Place on a PCB
* Open the 3D viewer
* Assert in CROUNDSEGMENT2D::CROUNDSEGMENT2D(): wxASSERT( aStart != aEnd );

This is presumably a zero-length segment between the radii.

Reproducing minimal PCB attached.

Workaround: use Oval pads.

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Application: kicad
Version: (6.0.0-rc1-dev-243-g539ca5aa3), debug build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.61.0 OpenSSL/1.1.0h zlib/1.2.11 libidn2/2.0.5 libpsl/0.20.2 (+libidn2/2.0.4) nghttp2/1.32.0
Platform: Linux 4.17.2-1-ARCH x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 2.24
    Boost: 1.67.0
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.60.0
    Compiler: GCC 8.1.1 with C++ ABI 1012

Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=OFF
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON