Add plane selection to allocating result_extent

src/encoder/writer.rs

@@ -240,8 +240,12 @@ fn encoder_on_short_writes() {
 
         write.inner.set_position(0);
         let mut tiff_reader = crate::decoder::Decoder::new(&mut write.inner).unwrap();
-        let data = tiff_reader.read_image().unwrap();
+        let mut data = tiff_reader.read_image().unwrap();
 
-        assert!(matches!(data, crate::decoder::DecodingResult::U8(v) if v == imgdata));
+        assert!(
+            matches!(&data, crate::decoder::DecodingResult::U8(v) if *v == imgdata),
+            "{data:?} @ {}",
+            data.as_buffer(0).byte_len()
+        );
     }
 }