Replace BeginMenu/MenuItem swapping g.NavWindow with a more adequate ImGuiItemFlags_NoWindowHoverableCheck.
Expecting more subtle issues to stem from this.
Note that NoWindowHoverableCheck is not supported by IsItemHovered() but then IsItemHovered() on BeginMenu() never worked: fix should be easy in BeginMenu() + add test is IsItemHovered(), will do later
ImGuiItemFlags_SelectableDontClosePopup=1<<5,// false // Disable MenuItem/Selectable() automatically closing their popup window
ImGuiItemFlags_MixedValue=1<<6,// false // [BETA] Represent a mixed/indeterminate value, generally multi-selection where values differ. Currently only supported by Checkbox() (later should support all sorts of widgets)
ImGuiItemFlags_ReadOnly=1<<7,// false // [ALPHA] Allow hovering interactions but underlying value is not changed.
ImGuiItemFlags_NoWindowHoverableCheck=1<<8,// false // Disable hoverable check in ItemHoverable()
// Controlled by widget code
ImGuiItemFlags_Inputable=1<<10,// false // [WIP] Auto-activate input mode when tab focused. Currently only used and supported by a few items before it becomes a generic feature.