fix(sdk-core): use explicit undefined check for mpcv2PartyId

Falsy check `params.mpcv2PartyId ? ... : 0` treats party ID 0 as
falsy, causing `getSignatureShareRoundOne` to receive `undefined`
while the `Dsg` constructor receives `0` when `mpcv2PartyId` is
not supplied. Replace with an explicit undefined check to ensure
both callers receive the same value.

Ticket: WAL-387

Author: zahin-mohammad

modules/sdk-core/src/bitgo/utils/tss/ecdsa/ecdsaMPCv2.ts

@@ -776,7 +776,7 @@ export class EcdsaMPCv2Utils extends BaseEcdsaUtils {
     const hashBuffer = hash.update(bufferContent).digest();
     const otherSigner = new DklsDsg.Dsg(
       userKeyShare,
-      params.mpcv2PartyId ? params.mpcv2PartyId : 0,
+      params.mpcv2PartyId !== undefined ? params.mpcv2PartyId : 0,
       derivationPath,
       hashBuffer
     );