[firestore] added missing conditional for firestore transaction error…

…s - should now error on failed promise validations

lib/modules/firestore/TransactionHandler.js

@@ -179,7 +179,7 @@ export default class TransactionHandler {
     // reject the final promise and remove from native
     // update is failed when either the users updateFunction
     // throws an error or rejects a promise
-    if (updateFailed) {
+    if (updateFailed || finalError) {
       // $FlowExpectedError: Reject will always be present
       return reject(finalError);
     }