Handle BitArray.setRange assertion better.

Author: isoos

app/lib/search/mem_index.dart

@@ -132,7 +132,7 @@ class InMemoryPackageIndex {
 
   PackageSearchResult search(ServiceSearchQuery query) {
     // prevent any work if offset is outside of the range
-    if ((query.offset ?? 0) > _documents.length) {
+    if ((query.offset ?? 0) >= _documents.length) {
       return PackageSearchResult.empty();
     }
     return _scorePool.withScore(

app/test/search/mem_index_test.dart

@@ -89,6 +89,12 @@ server.dart adds a small, prescriptive server (PicoServer) that can be configure
       index = InMemoryPackageIndex(documents: docs);
     });
 
+    test('empty index search', () {
+      final index = InMemoryPackageIndex(documents: []);
+      final rs = index.search(ServiceSearchQuery.parse(query: 'text'));
+      expect(rs.packageHits, isEmpty);
+    });
+
     test('package name match: async', () async {
       final PackageSearchResult result =
           index.search(ServiceSearchQuery.parse(query: 'async'));