sort: properly check for empty reads

src/uu/sort/src/chunks.rs

@@ -102,6 +102,7 @@ pub fn read(
         carry_over.clear();
         carry_over.extend_from_slice(&buffer[read..]);
 
+        if read != 0 {
             let payload = Chunk::new(buffer, |buf| {
                 let mut lines = unsafe {
                     // SAFETY: It is safe to transmute to a vector of lines with shorter lifetime,
@@ -112,7 +113,6 @@ pub fn read(
                 parse_lines(read, &mut lines, separator, &settings);
                 lines
             });
-        if !payload.borrow_lines().is_empty() {
             sender.send(payload).unwrap();
         }
         if !should_continue {

tests/by-util/test_sort.rs

@@ -800,3 +800,12 @@ fn sort_multiple() {
         .succeeds()
         .stdout_is("a\nb\nb\n");
 }
+
+#[test]
+fn sort_empty_chunk() {
+    new_ucmd!()
+        .args(&["-S", "40B"])
+        .pipe_in("a\na\n")
+        .succeeds()
+        .stdout_is("a\na\n");
+}