Fix memory leak in decode_webp #3355

Job	Run time
linux (linux.g5.4xlarge.nvidia.gpu, cuda, 11.8) / linux-job	9m 5s
linux (linux.12xlarge, cpu) / linux-job	4m 12s
macos (macos-m1-stable) / macos-job	2m 52s
windows (windows.4xlarge, cpu) / windows-job	19m 32s
windows (windows.g5.4xlarge.nvidia.gpu, cuda, 11.8) / windows-job	22m 48s
	58m 29s

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