Handle case where token map extends beyond last line of input (fixes #166).

lib/markdownlint.js

@@ -164,7 +164,7 @@ function annotateTokens(tokens, lines) {
       token.line = lines[token.map[0]];
       token.lineNumber = token.map[0] + 1;
       // Trim bottom of token to exclude whitespace lines
-      while (token.map[1] && !(lines[token.map[1] - 1].trim())) {
+      while (token.map[1] && !((lines[token.map[1] - 1] || "").trim())) {
         token.map[1]--;
       }
       // Annotate children with lineNumber

test/markdownlint-test.js

@@ -2628,3 +2628,32 @@ module.exports.markdownItPluginsMathjax =
       test.done();
     });
   };
+
+module.exports.markdownItPluginsMathjaxIssue166 =
+  function markdownItPluginsMathjaxIssue166(test) {
+    test.expect(2);
+    markdownlint({
+      "strings": {
+        "string":
+`## Heading
+
+$$
+1
+$$$$
+2
+$$`
+      },
+      "markdownItPlugins": [ [ pluginKatex ] ],
+      "resultVersion": 0
+    }, function callback(err, actual) {
+      test.ifError(err);
+      const expected = {
+        "string": {
+          "MD002": [ 1 ],
+          "MD041": [ 1 ]
+        }
+      };
+      test.deepEqual(actual, expected, "Unexpected issues.");
+      test.done();
+    });
+  };