fix(folderRoot): ensure folder URIs are consistently lowercased for cross-platform compatibility

Author: jackiotyu

src/core/folderRoot.ts

@@ -13,7 +13,7 @@ class WorkspaceFolderRoot implements vscode.Disposable {
     private checkUri() {
         const folders = vscode.workspace.workspaceFolders || [];
         this._folderSet = new Set(
-            folders.map((i) => i.uri.fsPath.replace(/\\/g, '/')).filter((i) => i),
+            folders.map((i) => (i.uri.fsPath || '').toLowerCase().replace(/\\/g, '/')).filter((i) => i),
         );
         // TODO Special handling for multiple workspaces
         if (folders.length) {