check for package lib exist before making package suggestions

pkg/analysis_server/lib/src/services/completion/import_uri_contributor.dart

Index: pkg/analysis_server/lib/src/services/completion/import_uri_contributor.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/import_uri_contributor.dart b/pkg/analysis_server/lib/src/services/completion/import_uri_contributor.dart
index 855185287347f864ff9db1d4ad0e777d2a0d1826..0d56e9810702d08e77c45a5a6ac861373a4579ca 100644
--- a/pkg/analysis_server/lib/src/services/completion/import_uri_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/import_uri_contributor.dart
@@ -137,7 +137,9 @@ class _ImportUriSuggestionBuilder extends SimpleAstVisitor {
         String prefix = 'package:$pkgName/';
         _addSuggestion(prefix);
         for (Folder folder in folders) {
-          _addPackageFolderSuggestions(partial, prefix, folder);
+          if (folder.exists) {
+            _addPackageFolderSuggestions(partial, prefix, folder);
+          }
         }
       });
     }