libedit: can't add alternate/DeMorgan body style

Description

It doesn't seem to be possible to add a new alternate body style in libedit.

Steps to reproduce

1. Open a symbol that doesn't have an alternate body style.
2. Open its properties, and check "Has alternate symbol (DeMorgan)
3. Click OK, note body style buttons on toolbar are still greyed out.
4. Open a symbol that already has an alternate body style, note that the buttons are now available

KiCad Version

Application: LibEdit
Version: (5.99.0-1530-ga06fa22b8), release build
Libraries:
    wxWidgets 3.0.5
    libcurl/7.70.0 OpenSSL/1.1.1g zlib/1.2.11 libidn2/2.3.0 libpsl/0.21.0 (+libidn2/2.2.0) libssh2/1.9.0 nghttp2/1.40.0
Platform: Linux 5.6.10-arch1-1 x86_64, 64 bit, Little endian, wxGTK
Build Info:
    Build date: May  5 2020 17:11:03
    wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
    Boost: 1.72.0
    OpenCASCADE Technology: 7.4.0
    Curl: 7.70.0
    Compiler: GCC 9.3.0 with C++ ABI 1013

Build settings:
    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=OFF
    KICAD_USE_OCC=ON
    KICAD_SPICE=ON