NuPlayerRenderer: Reset negative media time to zero

Reset negative media time to zero before call is made to
Mediaclock's setStartingTimeMedia().

Test:run android.mediastress.cts.HEVCR1080pAacLongPlayerTest#testPlay00 on gsi

Bug: 170621757
Bug: 171945667
Bug: 170797642
Bug: 171562715
Bug: 171850618
Change-Id: I2c405007b38229038119760423156bd53a2701c0