Skip repeated file syncs for libraries with no uploaded files

chrome/content/zotero/xpcom/storage.js

@@ -238,7 +238,9 @@ Zotero.Sync.Storage = new function () {
 				
 				// If we don't have any forced downloads, we can skip
 				// downloads if the last sync time hasn't changed
-				if (downloadAll && !downloadForced && lastSyncTime) {
+				// or doesn't exist on the server (meaning there are no files)
+				if (downloadAll && !downloadForced) {
+					if (lastSyncTime) {
 						var version = self.getStoredLastSyncTime(
 							libraryModes[libraryID], libraryID
 						);
@@ -249,6 +251,13 @@ Zotero.Sync.Storage = new function () {
 							downloadAll = false;
 						}
 					}
+					else {
+						Zotero.debug("No last " + libraryModes[libraryID].name
+							+ " sync time for library " + libraryID
+							+ " -- skipping file downloads");
+						downloadAll = false;
+					}
+				}
 				
 				if (downloadAll || downloadForced) {
 					Zotero.debug(downloadAll);