Use default volume description when missing label.

Some mounted storage volumes may not have a user-defined label.  In
those cases, use the default description for the volume.

Bug: 17781505
Change-Id: I8558ba2615c2ff2647a5d44afaec83249df466ab
diff --git a/packages/ExternalStorageProvider/src/com/android/externalstorage/ExternalStorageProvider.java b/packages/ExternalStorageProvider/src/com/android/externalstorage/ExternalStorageProvider.java
index c323a33..066acac 100644
--- a/packages/ExternalStorageProvider/src/com/android/externalstorage/ExternalStorageProvider.java
+++ b/packages/ExternalStorageProvider/src/com/android/externalstorage/ExternalStorageProvider.java
@@ -154,7 +154,12 @@
                 if (ROOT_ID_PRIMARY_EMULATED.equals(rootId)) {
                     root.title = getContext().getString(R.string.root_internal_storage);
                 } else {
-                    root.title = volume.getUserLabel();
+                    final String userLabel = volume.getUserLabel();
+                    if (!TextUtils.isEmpty(userLabel)) {
+                        root.title = userLabel;
+                    } else {
+                        root.title = volume.getDescription(getContext());
+                    }
                 }
                 root.docId = getDocIdForFile(path);
                 mRoots.add(root);