crash when opening a ngspice wbk from v6

Description

Steps to reproduce

1. open a simulation schematic comming from V6.0
2. Click [Inspect][Simulator...]
3. In the simulator window, click [File][Open Workbook...]
4. crash

KiCad Version

Application: KiCad x64 on x64

Version: (7.0.0-rc1-253-g7844602210), release build

Libraries:
	wxWidgets 3.2.1
	FreeType 2.12.1
	HarfBuzz 5.0.1
	FontConfig 2.14.1

Platform: Windows 11 (build 22621), 64-bit edition, 64 bit, Little endian, wxMSW

	wxWidgets: 3.2.1 (wchar_t,wx containers)
	Boost: 1.80.0
	OCC: 7.6.2
	Curl: 7.86.0-DEV
	ngspice: 38
	Compiler: Visual C++ 1934 without C++ ABI

Build settings:
	KICAD_SPICE=ON