Avoiding 'position' exceeds 'duration'.

In some cases Current position may exceed pre-calculated duration of movie,
resulting in corruptions on screen.
So limiting 'position' used for refresh of time bar.

Change-Id: Id286108181f0443adce932ac7478a8ad0e8e0283
Signed-off-by: Ruslan Shymkevych <x0153342@ti.com>