rpc: Fix for segfault if combinepsbt called with empty inputs

Author: benthecarman

src/rpc/rawtransaction.cpp

@@ -1514,6 +1514,9 @@ UniValue combinepsbt(const JSONRPCRequest& request)
     // Unserialize the transactions
     std::vector<PartiallySignedTransaction> psbtxs;
     UniValue txs = request.params[0].get_array();
+    if (txs.empty()) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, "Parameter 'txs' cannot be empty");
+    }
     for (unsigned int i = 0; i < txs.size(); ++i) {
         PartiallySignedTransaction psbtx;
         std::string error;

test/functional/rpc_psbt.py

@@ -269,6 +269,9 @@ def run_test(self):
             combined = self.nodes[2].combinepsbt(combiner['combine'])
             assert_equal(combined, combiner['result'])
 
+        # Empty combiner test
+        assert_raises_rpc_error(-8, "Parameter 'txs' cannot be empty", self.nodes[0].combinepsbt, [])
+
         # Finalizer test
         for finalizer in finalizers:
             finalized = self.nodes[2].finalizepsbt(finalizer['finalize'], False)['psbt']