Do not disable paste command when clipboard is empty

[Piotrek Koszuliński]

Paste command accepts data as an argument. It is very useful in case similar to pasting, like drag&drop. 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's also a bugfoot, because it's very hard to understand why I can't reproduce some issue any more.