Undo/redo shortcuts disabled after Preference reset (2.0 regression)

Steps to reproduce bug:
1. Edit > Preferences
2. Click "Reset All Preferences to Default"
3. Click "OK" to dismiss Preferences window
4. Try to use Ctrl+Z or Ctrl+Y with your current score. (Note: In the Edit menu the shortcuts do not appear next to the Undo and Redo menu items.)

Expected behavior: The standard shortcuts should continue to work even after a Preference reset.

Actual behavior: Undo and Redo shortcuts no longer work.

Workaround: If you restart MuseScore, the shortcuts start working again.

Tested using MuseScore 2.0.0 (Windows 7).