Don't use the application context to start the Accounts activity (because then we'd have to create a new task)

Fixes issue 2653

src/com/fsck/k9/activity/MessageList.java

@@ -3412,7 +3412,7 @@ public class MessageList
     {
         finish();
         // TODO inform user about account unavailability using Toast
-        Accounts.listAccounts(getApplicationContext());
+        Accounts.listAccounts(this);
     }
 
 }