clicking rejoin button does nothing when downloads arent complete

[Ruwetuin]

there is no feedback, which might frustrate new users who havent figured out how the download system works

[MasterBel2]

2 solutions I'm thinking of

1. Show an error message on button press
2. Disable the button and show a tooltip w/explanation on hover

I'd prefer 2 but I'm estimating 1 would be easier.