harden equality function

Author: kit-ty-kate

src/patch.ml

@@ -226,7 +226,7 @@ let operation_eq a b = match a, b with
   | Create a, Create b -> String.equal a b
   | Edit (a, a'), Edit (b, b')
   | Rename_only (a, a'), Rename_only (b, b') -> String.equal a b && String.equal a' b'
-  | _ -> false
+  | Delete _, _ | Create _, _ | Edit _, _ | Rename_only _, _ -> false
 
 let no_file = "/dev/null"