LibWeb: Correct generated image and ratio-only replaced sizing #33349

Job	Run time
Linux, arm64, Sanitizer, Clang / CI	21m 50s
Linux, x86_64, Fuzzers, Clang / CI	8m 21s
macOS, arm64, Sanitizer, Clang / CI	11m 5s
Linux, x86_64, All_Debug, Clang / CI	11m 8s
Linux, x86_64, Release, GNU / CI	11m 15s
Linux, x86_64, Sanitizer, Clang / CI	21m 44s
Windows, x86_64, Sanitizer, ClangCL / CI	13m 56s
	1h 39m 19s

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