Fix SWIZ-62 by ensuring bean source is not null before attempting tear down.

Author: brian428

src/org/swizframework/core/BeanFactory.as

@@ -380,6 +380,9 @@ package org.swizframework.core
  */
 public function tearDownBean( bean:Bean ):void
 {
+if( bean.source == null )
+return;
+
 for each( var processor:IProcessor in swiz.processors )
 {
 // skip factory processors