Fix: fall through to getRootNodes() when no progressive items arrive

After the 30s timeout, if no progressive notifications were received
(e.g., eclipse.jdt.ls progressive notifications not yet available),
fall through to the normal getRootNodes() path instead of returning
an empty array. This ensures the worst case matches today's behavior.

Addresses review comment from wenytang-ms.

Author: chagong

src/views/dependencyDataProvider.ts

@@ -152,7 +152,13 @@ export class DependencyDataProvider implements TreeDataProvider<ExplorerNode> {
                 const timeout = new Promise<void>((resolve) => setTimeout(resolve, 30_000));
                 await Promise.race([this._progressiveItemsReady, timeout]);
             }
-            return this._rootItems || [];
+            // If progressive items arrived, return them. Otherwise fall
+            // through to the normal getRootNodes() path so the tree is
+            // never left blank (e.g., when the JDTLS progressive
+            // notifications are not available yet).
+            if (this._rootItems && this._rootItems.length > 0) {
+                return this._rootItems;
+            }
         }
 
         const children = (!this._rootItems || !element) ?