SIGSEGV if HOME isn't defined (both stable and nightly)

Description

KiCad (and the Python API) dies with a segment violation if the HOME environment variable isn't defined.

I think this can be avoided, but KiCad should at least print an error and gracefully exit.

Steps to reproduce

1. Just run: HOME= kicad

KiCad Version

Application: Eeschema

Version: 5.99.0-unknown-84dd78e01d~106~ubuntu20.10.1, release build

Libraries:
	wxWidgets 3.0.5

Platform: Linux 5.9.0-5-amd64 x86_64, 64 bit, Little endian, wxGTK, gnome, x11

	wxWidgets: 3.0.5 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.71.0
	OCC: 7.4.0
	Curl: 7.68.0
	ngspice: 32
	Compiler: GCC 10.2.0 with C++ ABI 1014

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
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON