Crash in Symbol Editor

[Jorge Neiva]

The when the crash happens, the window gets busy. The only way to stop is terminating the window.
It don't generate segment fault.

How to reproduce:

Open Symbol Editor -> select any footprint -> select random pin -> right click and copy -> right click and paste -> place in anywhere then the window stops.

If its made by "Ctrl+V" and click any place it will have the same behavior.

Kicad Version:

Application: KiCad
Version: 6.0.0-unknown-dfc3a11~100~ubuntu18.04.1, release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.58.0 OpenSSL/1.1.0g zlib/1.2.11 libidn2/2.0.4 libpsl/0.19.1 (+libidn2/2.0.4) nghttp2/1.30.0 librtmp/2.3
Platform: Linux 4.15.0-50-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.22
    Boost: 1.65.1
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.58.0
    Compiler: GCC 7.4.0 with C++ ABI 1011

Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=ON
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON

[Jeff Young (jeyjey)]

Note: undo of a pin paste also doesn't work. (In fact, undo of paste doesn't work in LibEdit.)