This fixes failure to play the prologue video in Planet of the Apes: Last Frontier, which unpauses by calling Start() with a location. The exact state leading to this issue does not occur in the Start() tests, and it's not clear how to reproduce it reliably.
-- v7: mf: Do not count draining a downstream node as a request fulfillment. mf: Fill the sample request queue also when seeking while running. mf: Initialise the grabber sample count when setting state after a seek. mf/tests: Wait for session closure at the end of test_media_session_Start(). mf/tests: Test pause followed by immediate restart at current time in test_media_session_Start(). mf/tests: Test sample delivery where applicable in test_media_session_Start().