IBus is impossible for displays above 9

Hi

Please check this https://github.com/qt/qtbase/blob/5.9/src/plugins/platforminputcontexts/ibus/qibusplatforminputcontext.cpp#L574

need not it be displayNumber = display.right(display.length() - pos); instead ?

So when display is, eg. ':888' displayNumber becames '8', for 'unix:888' we get dispayNumber as 'x:888' which certainly stops IBus operation.

PS. It would be fine if you enable tickets on github as well, this interface is not very good and extremelly slow