Fixes #5577 

I decided to bubble up the error from where we actually try to load the
contract info. This helps to make sure that we don't miss some entry
point by accident. The draw back is that we have to live with some
additional `.expect`.

@pgherveou

 With this logic the proxy and its runtime part should be
completely unaware whether something is a contract call or a balance
transfer. They should just route everything into pallet_revive.

---------

Co-authored-by: Cyrill Leutwiler <cyrill@parity.io>