Add subsubifds test file

tests/COPYRIGHT

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+subsubifd.tif:
+  url: https://data.kitware.com/api/v1/file/hashsum/sha512/372ca32735c8a8fdbe2286dabead9e779da63f10ba81eda84625e5273f76d74ca1a47a978f67e9c00c12f7f72009c7b2c07a641e643bb0c463812f4ae7f15d6e/download
+  credit: https://github.com/DigitalSlideArchive/tifftools/commit/4d00c70dbce828262f86c1431f7c66b1748965ac
+  license: CC0

tests/subsubifds.rs

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+use tiff::{decoder::Decoder, tags::IfdPointer};
+
+// This file has the following IFD structure:
+//
+// ```
+// IFD -> IFD -> IFD
+//        |-> IFD
+//        |-> IFD -> IFD
+//        |          \-> IFD -> IFD
+//        \-> IFD
+// ```
+//
+// where the main chain of IFD has 3 images, the second of which has several sub-IFDs and some have
+// more nested IFDs.
+const TEST_IMAGE_SUBIFD: &str = "./tests/subsubifds.tif";
+use std::fs::File;
+
+#[test]
+fn decode_seek_chain() {
+    let file = File::open(TEST_IMAGE_SUBIFD).expect("Cannot open test image");
+    let mut decoder = Decoder::new(file).expect("Invalid format to create decoder");
+
+    decoder.next_image().unwrap();
+    decoder.next_image().unwrap();
+    assert!(!decoder.more_images());
+
+    // Ensure we can seek, to do this again.
+    decoder.seek_to_image(0)
+        .expect("Failed to seek to first image");
+    decoder.next_image().unwrap();
+    decoder.next_image().unwrap();
+    assert!(!decoder.more_images());
+}