webp frames iterator is now ending iteration if no more frames are decodable #1393

Job	Run time
Fuzz targets (afl)	2m 34s
build_benchmarks	52s
cargo-deny	22s
Fuzz targets (cargo-fuzz)	53s
clippy	2m 1s
public_private_dependencies	25s
rustfmt	17s
test_avif_decoding	1m 27s
test_features	19s
test_other_archs (powerpc-unknown-linux-gnu)	2m 39s
test_features (default)	1m 48s
test_toolchains (1.67.1)	32s
test_features (rayon)	21s
test_other_archs (i686-unknown-linux-gnu)	1m 32s
test_toolchains (nightly)	1m 59s
test_features (avif)	39s
test_toolchains (beta)	1m 21s
test_features (bmp)	17s
test_features (dds)	21s
test_features (exr)	29s
test_features (ff)	24s
test_features (gif)	18s
test_features (hdr)	22s
test_features (ico)	25s
test_features (jpeg)	20s
test_features (png)	22s
test_features (pnm)	24s
test_features (qoi)	18s
test_features (tga)	21s
test_features (tiff)	28s
test_features (webp)	37s
	25m 27s

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