Rearrange fillPSBT arguments

Move fillPSBT input-output argument before output-only arguments. This is a
temporary workaround which can go away with improvements to libmultiprocess
code generator. Currently code generator figures out order of input-output
parameters by looking at input list, but it would make more sense for it to
take order from output list, so input-only parameters still have to be first
but there is more flexibility for the other parameters.

src/interfaces/wallet.h

@@ -198,9 +198,9 @@ public:
     virtual TransactionError fillPSBT(int sighash_type,
         bool sign,
         bool bip32derivs,
+        size_t* n_signed,
         PartiallySignedTransaction& psbtx,
-        bool& complete,
-        size_t* n_signed) = 0;
+        bool& complete) = 0;
 
     //! Get balances.
     virtual WalletBalances getBalances() = 0;