Fix LoaderCallback.onLoadFinished uncalled issue

When two loaders started almost at the same time,
it is possible onLoadFinished is never called.

Bug: 260687359
Test: Unit tests passed and manual test on device
Merged-In: I41a041d5878f9930db44775408380d0d4588faba
Change-Id: I41a041d5878f9930db44775408380d0d4588faba
Signed-off-by: Zhenwei Chen <zhenwec@google.com>
(cherry picked from commit 41ce8772)