Get rid of unnecessary error branch

Author: mikesamuel

lib/es6/Lexer.js

@@ -80,10 +80,9 @@ function makeLexer () {
         ? DELIMITED_BODIES[delimiter]
         : PREFIX_BEFORE_DELIMITER;
       const match = pattern.exec(text);
-      if (!match) {
-        throw new Error(
-          errorMessage = msg`Failed to lex starting at ${text}`);
-      }
+      // Match must be defined since all possible values of pattern have
+      // an outer Kleene-* and no postcondition so will fallback to matching
+      // the empty string.
       let nConsumed = match[0].length;
       if (text.length > nConsumed) {
         const chr = text.charAt(nConsumed);