Fix get_image_metadata() for SVG Files

[Jieiku]

This is a fix for get_image_metadata() so that it returns the expected values for width and height of SVG files as discussed in #1877

I assumed this should be a pull request against the next branch, but I have no idea what amount of time goes by before these get merged into the current release.

I can also submit a pull request against the current branch if you like.

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Code changes

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• Are you doing the PR on the next branch?

If the change is a new feature or adding to/changing an existing one:

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[Keats]

Thanks!