Revert in C2T dispute

[dmaretskyi]

In the case there's a C2T transaction to a non-empty state leaf, the dispute would trigger a revert which makes it impossible to dispute this fradulent transaction.

Here's the line that triggers a dispute:

hubble-contracts/contracts/libs/Transition.sol

Line 99 in 0032354

require(

I think the fix would be to return an Ok/Error status like in the other processTransition* functions.