Accept page index 0 for getChildren() in MediaLibraryServiceLegacyStub

This is consistent with the new MediaSessionStub that accepts page index 0
and the JavaDoc of legacy and new service callbacks.

Issue: #32
PiperOrigin-RevId: 431390454
(cherry picked from commit 9821dd2)

libraries/session/src/main/java/androidx/media3/session/MediaLibraryServiceLegacyStub.java

@@ -198,7 +198,7 @@ public void onLoadChildren(
             try {
               int page = options.getInt(EXTRA_PAGE);
               int pageSize = options.getInt(EXTRA_PAGE_SIZE);
-              if (page > 0 && pageSize > 0) {
+              if (page >= 0 && pageSize > 0) {
                 // Requesting the list of children through pagination.
                 @Nullable
                 LibraryParams params =
@@ -223,7 +223,7 @@ public void onLoadChildren(
                   parentId,
                   /* page= */ 0,
                   /* pageSize= */ Integer.MAX_VALUE,
-                  /* extras= */ null);
+                  /* params= */ null);
           sendLibraryResultWithMediaItemsWhenReady(result, future);
         });
   }