802 fix color moved side by side panic (#803)

Append newline character when preparing raw line

Fixes #802

Author: dandavison

etc/examples/72-color-moved-4.diff

@@ -0,0 +1,8 @@
+diff --git a/file.py b/file.py
+index f2f1f5e..9735c3a 100644
+--- a/file.py
++++ b/file.py
+@@ -1,2 +1,2 @@
+-class X: pass  # • unicode
+ class Y: pass  # • unicode
++class X: pass  # • unicode

etc/examples/802-color-moved.diff

@@ -0,0 +1,12 @@
+commit 57e5082
+Author: Caleb Maclennan <caleb@alerque.com>
+Date:   Sat Nov 27 01:08:54 2021 +0300
+
+    Move verses to correct week file
+
+diff --git a/foo.md b/foo.md
+index ba489f0..0ad8245 100644
+--- a/foo.md
++++ b/foo.md
+@@ -20,3 +20,99 @@ foo bar
++As I swore in my wrath, 'They shall not enter my rest.'"

src/paint.rs

@@ -135,9 +135,13 @@ impl<'p> Painter<'p> {
         }
     }
 
-    // Remove initial -/+ character, and expand tabs as spaces, retaining ANSI sequences.
+    // Remove initial -/+ character, expand tabs as spaces, retaining ANSI sequences. Terminate with
+    // newline character.
     pub fn prepare_raw_line(&self, raw_line: &str) -> String {
-        ansi::ansi_preserving_slice(&self.expand_tabs(raw_line.graphemes(true)), 1)
+        format!(
+            "{}\n",
+            ansi::ansi_preserving_slice(&self.expand_tabs(raw_line.graphemes(true)), 1),
+        )
     }
 
     /// Expand tabs as spaces.