Synchronize H/V Scrolling commands remain enabled after closing a 2nd view

[alankilborn]

Description of the Issue

The View menu's Synchronize Vertical Scrolling and Synchronize Horizontal Scrolling commands are not correctly disabled when a two-view editing environment is reduced to a single view by closure of all files in a second view.

Steps to Reproduce the Issue

1. Start with a new 1 tab open (only) in a single view setup
2. Create a new tab with Ctrl+n; new 2 appears
3. Right-click the tab for new 2 and choose Move Document > Move to Other View; you now have one document in each view:
   
4. Observe that View menu's synchronized scrolling commands are enabled:
   
5. Right-click the new 2 tab and select Close and thus return to only having one view (the remaining view only has new 1 in it).

Expected Behavior

When examining the View menu after step 5 has been executed, I expect to see the highlighted menu items from the screenshot in step 4 to be disabled/greyed.

Actual Behavior

When examining the View menu after step 5 has been executed, the highlighted menu items from the screenshot in step 4 remain enabled.

Debug Information

Notepad++ v8.4.9 (64-bit)
Build time : Jan 27 2023 - 03:11:16
Path : W:\npp.misc_NoBackup\Releases\npp.8.4.9\npp.8.4.9.portable.x64\notepad++.exe
Command Line : -titleAdd="8.4.9 64-bit" -multiInst
Admin mode : OFF
Local Conf mode : ON
Cloud Config : OFF
OS Name : Windows 10 Enterprise (64-bit)
OS Version : 21H2
OS Build : 19044.2486
Current ANSI codepage : 1252
Plugins :
mimeTools (2.9)
NppConverter (4.5)
NppExport (0.4)
PythonScript (2)

[alankilborn]

This issue is a close-cousin to #5250