Fix the empty result issue in add -p (#664)

* Strip a neglected CR character in ingest_line

* Add test_orphan_carriage_return_is_stripped

* Eliminate redundant assignment in if-let-Some

src/delta.rs

@@ -184,6 +184,13 @@ impl<'a> StateMachine<'a> {
             .to_string()
         };
         self.line = ansi::strip_ansi_codes(&self.raw_line);
+
+        // Strip the neglected CR.
+        // (CR-LF is unfortunately split by git because it adds ansi escapes between them.
+        //  Thus byte_lines library can't remove the CR properly.)
+        if let Some(b'\r') = self.line.bytes().nth_back(0) {
+            self.line.truncate(self.line.len() - 1);
+        }
     }
 
     /// Should a handle_* function be called on this element?

src/tests/test_example_diffs.rs

@@ -296,6 +296,16 @@ commit 94907c0f136f46dc46ffae2dc92dca9af7eb7c2e
         );
     }
 
+    #[test]
+    fn test_orphan_carriage_return_is_stripped() {
+        let config = integration_test_utils::make_config_from_args(&[]);
+        let output = integration_test_utils::run_delta(
+            GIT_DIFF_SINGLE_HUNK_WITH_SEQUENCE_OF_CR_ESCAPE_SEQUENCES_LF,
+            &config,
+        );
+        assert!(output.bytes().all(|b: u8| b != b'\r'));
+    }
+
     #[test]
     fn test_commit_decoration_style_omit() {
         _do_test_commit_style_no_decoration(&[
@@ -1708,6 +1718,20 @@ Date:   Thu May 14 11:13:17 2020 -0400
  #[allow(dead_code)]
 ";
 
+    const GIT_DIFF_SINGLE_HUNK_WITH_SEQUENCE_OF_CR_ESCAPE_SEQUENCES_LF: &str = "\
+diff --git a/src/main.rs b/src/main.rs
+index f346a8c..e443b63 100644
+--- a/src/main.rs
++++ b/src/main.rs
+@@ -1,5 +1,4 @@
+-deleted line\r
+-\r
+ fn main() {\r
+     println!(\"existing line\");\r
++    println!(\"added line\");\r
+ }\r
+";
+
     const DIFF_IN_DIFF: &str = "\
 diff --git a/0001-Init.patch b/0001-Init.patch
 deleted file mode 100644