Eddsa gadget circuit is not correctly solved

[ThomasPiellard]

In r1cs.go, In the solveR1c method, when solving for a binary decomposition the solver checks if one of the bit is not already instantiated (it can be the case if we enforce a certain bit to be 1 for instance). In eddsa gadget, when solving the circuit, for the scalar multiplications, all the bits are falsely instantiated, so solveR1c does not solve them, and they all end up being 0.

Note: when removing the check if a wire is instantiate in solveR1c, the solver works.