Fix race condition on deleting clickedItem

[odinho]

If you have some code removing all items before the timeout is
able to run, you'll get a nasty TypeError if you don't null check
clickedItem.

[odinho]

I saw a lot of this error when trying to make our selenium tests be free of console errors. The exception message in Opera and Chromium-based browsers is:

TypeError: Cannot convert undefined or null to object

[isteven]

@odinho ,

Thanks for the PR. Can you ensure that this breaks none of the existing functionalities? If all are OK, I'm going to merge it.

[odinho]

I never got to write full tests. But it did not break any of the internal tests for Hola when I worked there, and this patch was (and still is) used for all their web pages and control panels. So it has seen a lot of use.

It shouldn't break something, but then maybe it will.