Fix IndexError when preprocessing an empty image or video list

[MohammadHijjawi97]

What does this PR do?

is_valid_image_imagelist([]) returns True because all([]) is True, so preprocess then crashes with IndexError on image[0] / video[0].

This rejects an empty list before that indexing path and raises a clear ValueError.

Fixes #14864

Tests

New tests fail on unmodified main (IndexError) and pass with the fix.

[github-actions]

Hi @MohammadHijjawi97, thanks for the PR! It does not appear to link an issue it fixes. If this PR addresses an existing issue, please add a closing keyword (e.g. Fixes #1234) to the PR description so the issue is linked. See the contribution guide for more details. If this PR intentionally does not fix a tracked issue, a maintainer can add the no-issue-needed label to silence this reminder.

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[MohammadHijjawi97]

Opened #14864 for this and linked it with Fixes #14864 in the description.