Merge #489: replaced if else return with mapping

480c3fd replaced if else return with mapping (BufferOverflow)

Pull request description:

  Fixes #479

ACKs for top commit:
  apoelstra:
    ACK 480c3fd

Tree-SHA512: 6b7384217ea1dbc621b26ca86fb2d6f9aa44f190b0b3abd20b5b4c8d1c659a274d3aab86223d58594d8a68ef34764f444d48c79f16e010c021351187c1b6b32e

src/descriptor/checksum.rs

@@ -166,11 +166,7 @@ impl<'f, 'a> Formatter<'f, 'a> {
 impl<'f, 'a> fmt::Write for Formatter<'f, 'a> {
     fn write_str(&mut self, s: &str) -> fmt::Result {
         self.fmt.write_str(s)?;
-        if self.eng.input(s).is_ok() {
-            Ok(())
-        } else {
-            Err(fmt::Error)
-        }
+        self.eng.input(s).map_err(|_| fmt::Error)
     }
 }