Improve test coverage when external preloaded task has a preload-task

The task which is being preloaded could have a preload-task itself.
Before this change, there was no test coverage for this use case.
Thus, add a test so that it continues to work as expected.

Change-Id: I50af50e3143c8b852e5ced71cf374ba8bc9376a1
1 file changed