Check item.payload.docs is iterable before iterating

Author: phillmac

src/DocumentIndex.js

@@ -13,7 +13,7 @@ class DocumentIndex {
 
   updateIndex (oplog, onProgressCallback) {
     const reducer = (handled, item, idx) => {
-      if (item.payload.op === 'PUTALL') {
+      if (item.payload.op === 'PUTALL' && item.payload.docs[Symbol.iterator]) {
         for (const doc of item.payload.docs) {
           if (handled[doc.key] !== true) {
             handled[doc.key] = true