Fix switching among buildmenu and gridmenu.

[saurtron]

Work done

• Fixes problems when switching between grid and buildmenu.

Explanation

• Both use the same global WG['buildmenu']. It will be set to nil by both on Shutdown and setup with Initialize, so this really needs DisableWidget to run immediately, and before WG['buildmenu'] is created. Otherwise it will get destroyed either in the middle of Initialize or afterwards by the other widget (they're fighting for the same global).
• Seems buildmenu->gridmenu broke with the new queued DisableWidget that will make shutdown run after initialize is done here. Looks like gridmenu->buildmenu was broken since some time (jun-2024 with 30cac26).