symbol editor segmentation fault trying to edit text field in new unit

Description

Current behavior: segmentation fault (core dumped) Expected behavior: Fiel properties dialog displayed

Steps to reproduce

1. Open symbol editor, load existing symbol with text field in first unit
2. Go to symbol properties dialog, increase number of units
3. Open newly added unit.
4. Double-click to text field

KiCad Version

Application: KiCad Symbol Editor

Version: (6.99.0-1809-gdfdedfa605), release build

Libraries:
	wxWidgets 3.0.4
	FreeType 2.10.1
	HarfBuzz 2.6.4
	FontConfig 2.13.1

Platform: Linux 5.13.0-40-generic x86_64, 64 bit, Little endian, wxGTK, cinnamon, x11

	wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
	Boost: 1.71.0
	OCC: 7.5.2
	Curl: 7.68.0
	ngspice: 31
	Compiler: GCC 9.4.0 with C++ ABI 1013

Build settings:
	KICAD_USE_OCC=ON
	KICAD_SPICE=ON