Regression: opening shared folders in My Computer takes too much time

To reproduce this:

1. Make sure you have some shared folders enabled in VirtualBox VM settings. If not, add any host folders on your desidion, then click APply and OK, to save the settings.
2. Install ReactOS in VirtualBox (settings does not matter).
3. In VirtualBox, connect Guest Additions ISO by choosing Devices -> Connect Guest Additions ISO.
4. In ReactOS, open My Computer, then CD-ROM device with Guest Additions.
5. Run VirtualBoxGuestAdditions.exe. It will run an appropriate x86 executable for the OS architecture.
6. Follow the install wizard by clicking Next a few times, use default settings.
7. Click Install.
8. After installing, choose Reboot Computer now and click Finish.
9. After reboot, open My Computer.
10. Double-click on any of network drives, which indicate shared folders added in step 1.

Up to 0.4.15-dev-7946-gc0c270e, shared folders are opening immediately, as they should.

Starting from 0.4.15-dev-7947-g91acf82, after double-click, opening takes long time. Shell completely hands and becomes unresponsive on ~55-60 seconds (nearly 1 minute), and mouse cursors looks as busy. Only after the time ends up, it continues the execution: responses again and opens needed shared folder as usually.

The guilty commit is definitely https://github.com/reactos/reactos/commit/91acf823d8d4e2b6b6e8012c98b1f178922b1547, because when using shell32.dll from 0.4.15-dev-7946, opening works immediately, but after replacing it back to the version from 0.4.15-dev-7947, opening hangs again by the same way. Actually, it was a fix for CORE-13950.

"Memory and speed optimization" mentioned in the commit, actually very decreases the performance instead.

However, nothing suspicious is displayed in the log. See debug.log and slow_opening_network_drives.webm video test as well.