Image with height defined in % resizes properly
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Checked the html in the github issue and the image looks like it is resized properly in Servo.
Fixed image resizing when height is specified in percentages.
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#11723 (github issue number if applicable).
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