Do not disable paste command when clipboard is empty

[Piotrek Koszuliński]

Paste command accepts data as an argument. It is very useful in cases similar to pasting, like a drag&drop feature. However, we're disabling paste command if clipboard is empty what... breaks d&d and some of our tests.

Disabling paste command when clipboard is empty makes only a minor feature, because most of the time clipboard isn't empty and usually one first copies something before he tries to paste it. But the disadvantage is big - it completely breaks useful paste command and usually it also means a bugfoot, because it's very hard to understand why reported issue can't be reproduced any more.