symbol editor crashes on editing a non-existing symbol from within eeschema

Description

From within eeschema trying to edit a symbol that does not exist in the referenced library results in a segmentation fault.

Steps to reproduce

1. When opening a (kicad 5) project into KiCAD 6.0.4 some symbol may not found. For example "https://github.com/iansbremner/ReAmiga-3000---KiCAD.git". The issue is however not project-specific.
2. pressing the "Edit Symbol ..." button: results in a segmentation fault. On windows with a different project, with different missing symbols the symbol editor manages to open its window before crashing.

This is the output of running "tools->Update symbols from libraries ...":

As a side note pressing "Edit Library Symbol ..." results in opening a new empty symbol library, which debatably is wrong as well. Graying out both buttons seems a more intuitive solution.

KiCad Version

Application: KiCad
Version: 6.0.4+dfsg-1+b1, release build
Libraries:
    wxWidgets 3.0.5
    libcurl/7.82.0 OpenSSL/1.1.1n zlib/1.2.11 brotli/1.0.9 zstd/1.4.9 libidn2/2.3.2 libpsl/0.21.0 (+libidn2/2.3.0) libssh2/1.10.0 nghttp2/1.43.0 librtmp/2.3 OpenLDAP/2.5.11
Platform: Linux 5.16.0-5-amd64 x86_64, 64 bit, Little endian, wxGTK, gnome-xorg, x11
Build Info:
    Date: Mar 28 2022 08:36:23
    wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
    Boost: 1.74.0
    OCC: 7.5.1
    Curl: 7.82.0
    ngspice: 36
    Compiler: GCC 11.2.0 with C++ ABI 1016
Build settings:
    KICAD_USE_OCC=ON
    KICAD_SPICE=ON

Windows: 

Application: KiCad (64 bit) Version: (6.0.4), release build Libraries: wxWidgets 3.1.5 libcurl/7.78.0-DEV Schannel zlib/1.2.11

Platform: Windows 10 (build 19044) 64 bit edition, 64 bit, Little endian, wxMSW Build Info: Date: Mar 18 2022 03:04:44 wxWidgets: 3.1.5 (wchar_t,wx containers) Boost: 1.76.0 OCC: 7.6.0 Curl: 7.78.0-DEV ngspice: 36 Compiler: Visual C++ 1928 without C++ ABI Build settings: KICAD_USE_OCC=ON KICAD_SPICE=ON