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.
-- v6: mf: Reset transform nodes when seeking. mf: Initialise the grabber sample count when setting state after a seek. mf: Set pending requests for transform outputs to zero on flush. mf: Reset transform node outputs when seeking. mf: Flush nodes before restarting a paused source at a specific position. mf: Drop transform node input events when unpausing at a specific position. mf: Reset transforms before restarting a paused source instead of after. mf: Move transform node reset to a helper function.