Crash in design block adapter after adding non-existant project library

Description

Thread 0 Crashed::  Dispatch queue: com.apple.main-thread
0   libkicommon.8.99.0.dylib      	       0x1049c9afc LIB_TABLE::GetLogicalLibs() + 88
1   _eeschema.kiface              	       0x1125a4b6c DESIGN_BLOCK_TREE_MODEL_ADAPTER::AddLibraries(EDA_BASE_FRAME*) + 96
2   _eeschema.kiface              	       0x11253be6c PANEL_DESIGN_BLOCK_CHOOSER::RefreshLibs(bool) + 420
3   _eeschema.kiface              	       0x1125a11f0 SCH_EDIT_FRAME::KiwayMailIn(KIWAY_EXPRESS&) + 176

Steps to reproduce

1. Open schematic editor standalone
2. Open a project
3. Add a row to the project-specific symbol library table, containing a filename that doesn't exist
4. Accept the dialog
5. Open the library table dialog again
6. Accept the dialog again
7. Crash

KiCad Version

Application: KiCad arm64 on arm64

Version: 9.0.0-rc2, release build

Libraries:
	wxWidgets 3.2.6
	FreeType 2.13.3
	HarfBuzz 10.2.0
	FontConfig 2.15.0

Platform: macOS Sonoma Version 14.7.2 (Build 23H311), 64 bit, Little endian, wxMac

	wxWidgets: 3.2.6 (wchar_t,wx containers)
	Boost: 1.87.0
	OCC: 7.8.1
	Curl: 8.7.1
	ngspice: 44
	Compiler: Clang 16.0.0 with C++ ABI 1002
	KICAD_IPC_API=ON