Delays with QClipboard and "useEventLoop"

If LibreOffice is running with KDE integration and KFileDialog is open, if clipboard contents are held by LO (i.e. Ctrl+C in LO before the dialog is opened), then there is a visible delay when moving the mouse over the dialog contents. This is because KFileDialog repeatedly checks clipboard contents and these checks take visibly long (and there's not so few of them).

LO/Qt integration needs to set QClipboard to "useEventLoop" mode. The code there adds 50ms delay to every single clipboard data fetch, presumably to avoid busy-looping, but it's quite long and often needless.

The attached patch avoids any visible delay in the KFileDialog in this case.