Crash opening schematics with sheet field variables on labels

Steps to reproduce

Open attached project. Crash

Bisected to e4aa8278 @mroszko

crash.zip

KiCad Version

Application: KiCad x86_64 on x86_64

Version: 9.99.0-2713-g4c5b44545f, debug build

Libraries:
	wxWidgets 3.2.6
	FreeType 2.13.3
	HarfBuzz 10.2.0
	FontConfig 2.15.0

Platform: Ubuntu 25.04, 64 bit, Little endian, wxGTK, X11, KDE, x11
OpenGL: NVIDIA Corporation, NVIDIA GeForce RTX 3090/PCIe/SSE2, 4.6.0 NVIDIA 580.82.07

	wxWidgets: 3.2.6 (wchar_t,wx containers) GTK+ 3.24
	Boost: 1.83.0
	OCC: 7.8.1
	Curl: 8.12.1
	ngspice: 44.2
	Compiler: Clang 20.1.2 with C++ ABI 1002

Build settings:
	KICAD_IPC_API=OFF
	KICAD_USE_PCH=OFF
	KICAD_STDLIB_DEBUG=OFF
	KICAD_STDLIB_LIGHT_DEBUG=OFF
	KICAD_SANITIZE_ADDRESS=OFF
	KICAD_SANITIZE_THREADS=OFF

Locale: 
	Lang: en_US
	Enc: UTF-8
	Num: 1,234.5
	Encoded кΩ丈: D0BACEA9E4B888 (sys), D0BACEA9E4B888 (utf8)