Fix UtilityUnitTests.testSpecialIcons

Now non-special mailboxes on mailbox list doesn't have an icon, so
getIcon(Mailbox.TYPE_MAIL) should return null.

Change-Id: I354551baa4027c8e90c499dafac72423343c9cee

tests/src/com/android/email/UtilityUnitTests.java

@@ -124,14 +124,15 @@ public class UtilityUnitTests extends AndroidTestCase {
         // Make sure they're unique
         Set<Drawable> set = new HashSet<Drawable>();
         set.add(inbox);
-        set.add(mail);
         set.add(parent);
         set.add(drafts);
         set.add(outbox);
         set.add(sent);
         set.add(trash);
         set.add(junk);
-        assertEquals(8, set.size());
+        assertEquals(7, set.size());
+
+        assertNull(mail);
     }
 
     private static byte[] b(int... array) {