Simulation does not work with UNC paths [MSW-specific?]

Description

When a simulation model is accessed via a UNC path (e.g. \\server\sharename\folder\foo\bar.lib), ngspice cannot load that model.

Steps to reproduce

  1. Use windows
  2. Make a new project that is stored on a network share
  3. Copy a spice model (.lib file) into the project folder
  4. Add this model to a existing symbol
  5. Run the simulation
  6. The simulation command has a .include "//server/data/Benutzer/cpresser/Documents/_Projekte/hodoscope/pulse-generator-sim/max9000.lib" line in it. It does not process this.

KiCad Version

Application: KiCad x64 on x64

Version: 7.0.7, release build

Libraries:
    wxWidgets 3.2.2
    FreeType 2.12.1
    HarfBuzz 6.0.0
    FontConfig 2.14.1
    libcurl/7.88.1-DEV Schannel zlib/1.2.13

Platform: Windows 10 (build 19045), 64-bit edition, 64 bit, Little endian, wxMSW

Build Info:
    Date: Aug 14 2023 02:42:39
    wxWidgets: 3.2.2 (wchar_t,wx containers)
    Boost: 1.81.0
    OCC: 7.7.1
    Curl: 7.88.1-DEV
    ngspice: 40
    Compiler: Visual C++ 1936 without C++ ABI

Build settings:
    KICAD_SPICE=ON 
```d
Edited by Jeff Young