This event is fired when the players gear changes.
PLAYER_EQUIPMENT_CHANGED: equipmentSlot, hasCurrent
- number - InventorySlotId
- boolean - True when a slot becomes empty, false when filled.
- The second payload value was historically documented doing the reverse; true (1) when filled or false (nil) otherwise. 
- Modern FrameXML code labels the payload hasCurrent but does not actually use this payload, so the developer intent is unclear.
- It is unknown if the return values in fact 'flipped' at some point, or if the early documentation was simply wrong.