Fix possible array-out-of-bounds access, add test.

lib/markdownlint.js

@@ -65,7 +65,7 @@ function lintContent(content, config) {
       token.line = lines[token.map[0]];
       token.lineNumber = token.map[0] + 1;
       // Trim bottom of token to exclude whitespace lines
-      while (!(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

@@ -189,6 +189,30 @@ module.exports.stringInputLineEndings = function stringInputLineEndings(test) {
   });
 };
 
+module.exports.inputOnlyNewline = function inputOnlyNewline(test) {
+  test.expect(2);
+  var options = {
+    "strings": {
+      "cr": "\r",
+      "lf": "\n",
+      "crlf": "\r\n"
+    },
+    "config": {
+      "default": false
+    }
+  };
+  markdownlint(options, function callback(err, actualResult) {
+    test.ifError(err);
+    var expectedResult = {
+      "cr": {},
+      "lf": {},
+      "crlf": {}
+    };
+    test.deepEqual(actualResult, expectedResult, "Undetected issues.");
+    test.done();
+  });
+};
+
 module.exports.defaultTrue = function defaultTrue(test) {
   test.expect(2);
   var options = {