PCB editor crashes while importing Altium PcbDoc
# Description
PCB editor version 8.0.0 crashes while importing PcbDoc from Altium.
With the pcb editor version 7.0.0 the crash does not happen but for the same file a warning is displayed: "Altium layer (70) has no KiCad equivalent. It has been moved to KiCad layer Eco1_User."
# Steps to reproduce
1. open pcb editor
2. goto file/import and select Non-KiCad Board File
3. select the Altium .PcbDoc file and open it (unfortunately i can not share the file)
4. After loading polygons the pcb editor crashes
# KiCad Version
```
Application: KiCad PCB Editor x64 on x64
Version: 8.0.0, release build
Libraries:
wxWidgets 3.2.4
FreeType 2.12.1
HarfBuzz 8.3.0
FontConfig 2.14.2
libcurl/8.5.0-DEV Schannel zlib/1.3
Platform: Windows 10 (Erzeugungsversion 19045), 64-bit Edition, 64 bit, Little endian, wxMSW
Build Info:
Date: Feb 23 2024 02:24:15
wxWidgets: 3.2.4 (wchar_t,wx containers)
Boost: 1.83.0
OCC: 7.7.1
Curl: 8.5.0-DEV
ngspice: 42
Compiler: Visual C++ 1936 without C++ ABI
Build settings:
```
issue