Fix #37097: Setting scene frame does not update active camera

The issue was caused by uncertainty of current camera when
there're no markers to the left of current frame.

Now in this case camera from the top-left marker will be used.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@60822 954f8c5b-7b00-dc11-b283-0030488c597c