lag when closing preferences on windows when unreachable network drives present

### Problem description

### Problem:
Since at least v1.0.x and thru 1.1.1 stable (portable or installed) on windows11, I get a 15-45 sec lag when closing preferences.

### Differential:
After rounds of AI-helped trouble-shooting, safe-mode, clean installs, etc., etc, a virgin acct profile still had no lag while my profile did. This was across two windows11 machines with my profile. No files are used by FreeCAD on any network share.

### Workaround:
Disconnecting all unreachable network shares was the only thing that stopped the lag on my profile, which is terribly inconvenient to have to run a script to remap accessible drives when moving between work and home.

### Workbench affected?

Core (App, Gui,...)

### Steps to reproduce

Map a network drive on a VPN and turn off the tunnel.

### Expected behavior

Close prefs file and go back to work.

### Actual behavior

Close prefs file and wait through main window not responding for 15-45 sec.

### Development version About Info (in Safe Mode)

```shell
OS: Windows 11 build 26200
Architecture: x86_64
Version: 1.1.1.20260414 (Git shallow)
Build date: 2026/04/14 22:09:59
Build type: Release
Branch: (HEAD detached at 0108fd4b4)
Hash: 0108fd4b4850cc46e625b60e53cea7a7bbe69f8d
Python 3.11.15, Qt 6.8.3, Coin 4.0.3, Vtk 9.3.1, boost 1_86, Eigen3 3.4.0, PySide 6.8.3
shiboken 6.8.3, xerces-c 3.3.0, IfcOpenShell 0.8.4, OCC 7.8.1
Locale: English/United States (en_US)
Navigation Style/Orbit Style/Rotation Mode: CAD/Rounded Arcball/Window center
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Light/
Logical DPI/Physical DPI/Pixel Ratio: 96/141.951/1
```

### Last known good version (optional)

```shell
0.19 portable did not have this issue.
```

No source file or test is named. First reproduce on Windows 11 with an unreachable mapped network drive and preferences open, then trace the preferences-close path while measuring the 15–45 second stall. Done means closing preferences returns promptly without requiring network-drive remapping, with regression coverage for the disconnected-drive case.

Written by the indexing model from the issue text.