pcbnew crashes when checking footprint warnings

Description

pcbnew crashes when checking footprint warnings

Steps to reproduce

1. Create a project and board for which DRC gives footprint warnings
2. Run DRC
3. Click on the Footprint Warnings tab

KiCad Version

Application: Pcbnew
Version: (5.99.0-1128-g37eb13353f), release build
Libraries:
    wxWidgets 3.1.3
    libcurl/7.58.0 OpenSSL/1.1.1 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 5.3.0-42-generic x86_64, 64 bit, Little endian, wxGTK
Build Info:
    Build date: Mar 20 2020 19:11:31
    wxWidgets: 3.1.3 (wchar_t,wx containers) GTK+ 3.22
    Boost: 1.65.1
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.58.0
    Compiler: GCC 7.5.0 with C++ ABI 1011

Build settings:
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=OFF
    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