V 9.0.3 wrong netclass assigment when more than four netclasses

Description

Kicad V9.0.3 made a wrong netclass assignment when there are more than four netclasses.

Netlist names

Wrong pick-up netlist name

Steps to reproduce

1. Create a new project
2. Open Schematic Editor and create a connector with six pins
3. In Schematic, connect pins and place a net label
4. Open PCBEditor and update board from schematic to import footprints
5. In PCBEditor, create the netclasses and made a netclasses assignment.

Attached sample project: Kicad_test.zip

KiCad Version

Application: KiCad PCB Editor x86_64 on x86_64
Version: 9.0.3+1, release build
Libraries:
    wxWidgets 3.2.2
    FreeType 2.12.1
    HarfBuzz 6.0.0
    FontConfig 2.14.1
    libcurl/7.88.1 OpenSSL/3.0.17 zlib/1.2.13 brotli/1.0.9 zstd/1.5.4 libidn2/2.3.3 libpsl/0.21.2 (+libidn2/2.3.3) libssh2/1.10.0 nghttp2/1.52.0 librtmp/2.3 OpenLDAP/2.5.13
Platform: Debian GNU/Linux 12 (bookworm), 64 bit, Little endian, wxGTK, X11, KDE, wayland
OpenGL: Intel, Mesa Intel(R) Xe Graphics (TGL GT2), 4.6 (Compatibility Profile) Mesa 22.3.6
Build Info:
    Date: Aug 16 2025 11:40:45
    wxWidgets: 3.2.2 (wchar_t,wx containers) GTK+ 3.24
    Boost: 1.74.0
    OCC: 7.6.3
    Curl: 7.88.1
    ngspice: 39
    Compiler: GCC 12.2.0 with C++ ABI 1017
    KICAD_IPC_API=ON
Locale: 
    Lang: en_US
    Enc: UTF-8
    Num: 1.234,5
    Encoded кΩ丈: D0BACEA9E4B888 (sys), D0BACEA9E4B888 (utf8)

Update

You can have more than four netclasses, but the problem happens when you use (made a class assignment) more than four netclasses.

I tested KiCad 9.0.4 in another Linux version (fresh installation), and have the same problem.

Application: KiCad PCB Editor x86_64 on x86_64

Version: 9.0.4-9.0.4-0~ubuntu24.04.1, release build

Libraries:
	wxWidgets 3.2.4
	FreeType 2.13.2
	HarfBuzz 8.3.0
	FontConfig 2.15.0
	libcurl/8.5.0 OpenSSL/3.0.13 zlib/1.3 brotli/1.1.0 zstd/1.5.5 libidn2/2.3.7 libpsl/0.21.2 (+libidn2/2.3.7) libssh/0.10.6/openssl/zlib nghttp2/1.59.0 librtmp/2.3 OpenLDAP/2.6.7

Platform: Ubuntu 24.04.3 LTS, 64 bit, Little endian, wxGTK, X11, KDE, x11
OpenGL: Intel, Mesa Intel(R) HD Graphics 3000 (SNB GT2), 3.3 (Compatibility Profile) Mesa 25.0.7-0ubuntu0.24.04.2

Build Info:
	Date: Aug 18 2025 02:17:55
	wxWidgets: 3.2.4 (wchar_t,wx containers) GTK+ 3.24
	Boost: 1.83.0
	OCC: 7.6.3
	Curl: 8.5.0
	ngspice: 42
	Compiler: GCC 13.3.0 with C++ ABI 1018
	KICAD_IPC_API=ON

Locale:
	Lang: pt_BR
	Enc: UTF-8
	Num: 1.234,5
	Encoded кΩ丈: D0BACEA9E4B888 (sys), D0BACEA9E4B888 (utf8)