fix(sync_service): don't rethrow error when download fails

Download can fail if the file is not found on the server. In this case,
we should just return null and let the caller handle the error.

lib/sync/repository/src/google_drive.dart

@@ -14,10 +14,7 @@ class GoogleDrive implements SyncRepository {
   @override
   Future<List<int>?> download({required String fileName}) async {
     final fileId = await _getFileId(fileName);
-
-    if (fileId == null) {
-      throw SyncException('File does not exist.');
-    }
+    if (fileId == null) return null;
 
     final Media media;
     try {
@@ -26,9 +23,7 @@ class GoogleDrive implements SyncRepository {
         downloadOptions: DownloadOptions.fullMedia,
       ) as Media;
     } on DetailedApiRequestError catch (e) {
-      if (e.status == io.HttpStatus.notFound) {
-        throw SyncException('File does not exist.');
-      }
+      log.e('Failed to download file', e);
       return null;
     }
 

lib/sync/sync_service.dart

@@ -78,18 +78,12 @@ class SyncService {
   ///
   /// Throws a [SyncException] if an error occurs.
   Future<SyncData?> _downloadSyncData() async {
-    try {
-      final cloudSyncDataBytes = await _syncRepository.download(
-        fileName: kSyncDataFileName,
-      );
+    final cloudSyncDataBytes = await _syncRepository.download(
+      fileName: kSyncDataFileName,
+    );
 
-      if (cloudSyncDataBytes != null) {
-        return SyncData.fromBytes(cloudSyncDataBytes);
-      }
-    } on SyncException catch (e) {
-      throw SyncException(
-        'Failed to download sync data from cloud service: ${e.message}',
-      );
+    if (cloudSyncDataBytes != null) {
+      return SyncData.fromBytes(cloudSyncDataBytes);
     }
 
     return null;