fix(jqLite): ignore incompatible nodes on find()

When a jqLite collection contains text nodes, find() does not work :-(

This fix ignores all nodes than can't do getElementsByTagName()

It seems a little bit faster than testing nodeType : http://jsperf.com/nodetype-vs-duck-typing

Closes angular#4120

src/jqLite.js

@@ -822,7 +822,11 @@ forEach({
   },
 
   find: function(element, selector) {
-    return element.getElementsByTagName(selector);
+    if (element.getElementsByTagName) {
+      return element.getElementsByTagName(selector);
+    } else {
+      return [];
+    }
   },
 
   clone: jqLiteClone,

test/jqLiteSpec.js

@@ -1335,6 +1335,12 @@ describe('jqLite', function() {
       expect(innerDiv.length).toEqual(1);
       expect(innerDiv.html()).toEqual('text');
     });
+
+    it('should find child by name and not care about text nodes', function() {
+      var divs = jqLite('<div><span>aa</span></div>text<div><span>bb</span></div>');
+      var innerSpan = divs.find('span');
+      expect(innerSpan.length).toEqual(2);
+    });
   });