Fix disabled server browser tabs being restored as enabled

[HeresHavi]

Summary

Fixed server browser tabs configured with disabled="1" being restored as enabled.

Tabs using disabled="0" or no disabled attribute remain enabled, and normal shutdown now preserves the intended state.

Motivation

The saved value describes whether a tab is disabled, but it was passed directly to SetEnabled, which expects the opposite value. This inverted the tab state when MTA loaded its configuration.

For example, someone could disable the Local server browser tab in coreconfig.xml, launch MTA, and find that the tab was still usable. Closing MTA could then remove the original setting because the incorrect state was saved back.

Fixes #5031.

Test plan

Runtime

• Before Fix: disabled="1" left the Local tab enabled, and normal shutdown removed the attribute.
• After Fix: disabled="1" disabled the Local tab and remained saved after shutdown.
• Inverse Control: disabled="0" previously disabled the tab but now leaves it enabled.
• Valid Case: A missing disabled attribute left all server browser tabs enabled.
• Other Tabs: Internet, Favourites, and Recent remained usable while Local was disabled.
• Persistence: Confirmed the redundant disabled="0" attribute was removed during normal shutdown without changing the enabled state.

Builds and Tests

• Debug | Win32: Client Core build passed, 304 client tests passed.
• Release | Win32: Full solution build passed, 304 client tests passed.

Checklist

• Your code should follow the coding guidelines.
• Smaller pull requests are easier to review. If your pull request is beefy, your pull request should be reviewable commit-by-commit.