fix framerate detection again (really, i mean it this time)

fix framerate detection again (really, i mean it this time)
integer overflow was causing our sanity checks of ffmpegs frame rate
to fail.  We would then fall back to using less accurate values.

Also removes the completely incorrect adjustment that I made based on
ticks_per_frame.  That is only useful in a different code path.

git-svn-id: svn://localhost/HandBrake/trunk@3650 b64f7644-9d1e-0410-96f1-a4d463321fa5