fix: allow mailmaps to change the email by name and email (#1417)

Author: Byron

gix-mailmap/src/parse.rs

@@ -77,6 +77,9 @@ fn parse_line(line: &BStr, line_number: usize) -> Result<Entry<'_>, Error> {
         (Some(proper_name), Some(proper_email), Some(commit_name), Some(commit_email)) => {
             Entry::change_name_and_email_by_name_and_email(proper_name, proper_email, commit_name, commit_email)
         }
+        (None, Some(proper_email), Some(commit_name), Some(commit_email)) => {
+            Entry::change_email_by_name_and_email(proper_email, commit_name, commit_email)
+        }
         _ => {
             return Err(Error::Malformed {
                 line_number,