Move button-event reporting behind pointer-position update.
This is just a quickfix to restore correct pointer emulation with
dde_linux usb_drv. It does not change usb_hid_drv because the approach
is a questionable workaround of the current input event handling, which
reports events promptly on occurrence of inputs events and ignores
synchronization events completely. The original contrib code reported
the button press before absolute x and y positioning followed by a sync
event.
Issue #3019
Christian Helmuth