Fix tail -c panics when requested bytes exceed file size (#10268)

* Fix tail -c panics when requested bytes exceed file size

* Add tail bytes exceed file size test

* Update test to hit block size condition

src/uu/tail/src/tail.rs

@@ -473,7 +473,9 @@ fn bounded_tail(file: &mut File, settings: &Settings) {
             return;
         }
         FilterMode::Bytes(Signum::Negative(count)) => {
-            file.seek(SeekFrom::End(-(*count as i64))).unwrap();
+            if file.seek(SeekFrom::End(-(*count as i64))).is_err() {
+                file.seek(SeekFrom::Start(0)).unwrap();
+            }
             limit = Some(*count);
         }
         FilterMode::Bytes(Signum::Positive(count)) if count > &1 => {

tests/by-util/test_tail.rs

@@ -5040,6 +5040,22 @@ fn tail_n_lines_with_emoji() {
         .stdout_only("💐\n");
 }
 
+#[test]
+fn test_tail_bytes_exceeds_file_size() {
+    let ts = TestScenario::new(util_name!());
+    let at = &ts.fixtures;
+
+    // Should be > 4096 bytes (block size can vary):
+    at.write("test_file.txt", &"x".repeat(5000));
+
+    ts.ucmd()
+        .arg("-c")
+        .arg("1048576")
+        .arg("test_file.txt")
+        .succeeds()
+        .stdout_only("x".repeat(5000));
+}
+
 #[test]
 #[cfg(target_os = "linux")]
 fn test_follow_pipe_f() {