templater: eliminate whitespace nodes from parse tree

src/template.pest

@@ -17,7 +17,7 @@
 // predecessors % ("predecessor: " commit_id)
 // parents % (commit_id " is a parent of " super.commit_id)
 
-whitespace = { " " | "\n" }
+whitespace = _{ " " | "\n" }
 
 escape = @{ "\\" ~ ("n" | "\"" | "\\") }
 literal_char = @{ !("\"" | "\\") ~ ANY }

src/template_parser.rs

@@ -374,7 +374,7 @@ fn parse_commit_template_rule<'a>(
             }
             Box::new(ListTemplate(formatters))
         }
-        _ => Box::new(Literal(String::new())),
+        other => panic!("unexpected template rule: {other:?}"),
     }
 }