fix File-Header rule

src/rules/fileHeaderRule.ts

@@ -53,7 +53,7 @@ class FileHeaderWalker extends Lint.RuleWalker {
             } else {
                 // either the third or fourth capture group contains the comment contents
                 const comment = match[2] ? match[2] : match[3];
-                if (comment.search(this.headerRegexp) < 0) {
+                if (comment !== undefined && comment.search(this.headerRegexp) < 0) {
                     this.addFailureAt(offset, 0, Rule.FAILURE_STRING);
                 }
             }

test/rules/file-header/empty-file/test.js.lint

@@ -0,0 +1 @@
+// empty.

test/rules/file-header/empty-file/test.ts.lint

@@ -0,0 +1 @@
+// empty.

test/rules/file-header/empty-file/tslint.json

@@ -0,0 +1,8 @@
+{
+    "rules": {
+        "file-header": [true, "Good header \\d"]
+    },
+    "jsRules": {
+        "file-header": [true, "Good header \\d"]
+    }
+}