While passing in multiple files is supported, scrubbing both images
an movies wasn't working properly when multiple files were passed in.
For images, arguments such as "*.png" expand to multiple image files
which were each assigned a frame index of 0, this would play but stopped
scrubbing from working completely.
For movies, passing in multiple files would play back all files but
only properly scrub the first file, if other videos were longer than
the first scrubbing would jump to those.
Resolve by starting the frame index where the previous files left off.
Also resolve divide by zero when showing the indiciator for a single
frame.
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