Don't show a link preview for empty links

When hovering over a link without a target, qt5 will report the link target to be "1", which is wrong.
To work around this, we manually check if the link is "1" and if it is, we discard it.
In theory, this means that we won't get a preview for any link that actually *is* "1", but why would any link be "1"?

It's not worth reporting this to Qt since it seems fixed in Qt6

BUG: 456877