crash in symbol editor due to nullptr dereference

Description

opening symbol for editing from eeschema, removing a pin and adding it back crashes kicad

Steps to reproduce

1. open the attached project schematics
2. select the symbol and open it for editing with "Edit with Symbol Editor"
3. select pin2 and delete it
4. save the symbol -> schematics symbol updates correctly
5. add new pin with same name and pin number (pin2, 2)
6. save the symbol -> kicad crashes

symbol-editor-crash.zip

RemovingAndAddingPinCrash.avi

KiCad Version

Application: KiCad x86_64 on x86_64

Version: 8.99.0-1022-gb9b19cb5fb, release build

Libraries:
	wxWidgets 3.2.2
	FreeType 2.13.1
	HarfBuzz 8.0.1
	FontConfig 2.14.2

Platform: Ubuntu 23.10, 64 bit, Little endian, wxGTK, X11, mate, x11

	wxWidgets: 3.2.2 (wchar_t,wx containers) GTK+ 3.24
	Boost: 1.74.0
	OCC: 7.6.3
	Curl: 8.2.1
	ngspice: 42+
	Compiler: GCC 13.2.0 with C++ ABI 1018

Locale: 
	Lang: en_US
	Enc: UTF-8
	Num: 1 234,5