Add support for a without href, without children

Author: wooorm

handlers/link.js

@@ -6,7 +6,7 @@ var all = require('../all');
 
 function link(h, node) {
   var props = {
-    url: node.properties.href,
+    url: node.properties.href || '',
     title: node.properties.title || null
   };
 

tests/fixtures/a/index.html

@@ -1,2 +1,4 @@
 <p><a href="http://example.com" title="example">example</a></p>
-<p><a href="http://example.com">example</a></p>
+<p><a href="http://example.com">example</a></p>
+<p><a>example</a></p>
+<p><a></a></p>

tests/fixtures/a/index.md

@@ -1,3 +1,7 @@
 [example](http://example.com "example")
 
 [example](http://example.com)
+
+[example](<>)
+
+[](<>)