Updated libXi to 1.7.8.

This release fixes a crash introduced in the 1.7.7 release. If a device has
no classes, a wrong error was returned, eventually causing some applications
to crash. This is fixed now.

Niels Ole Salscheider (1):
      SizeClassInfo can return 0 even without an error

Peter Hutterer (2):
      XListInputDevices: don't touch ndevices in case of error
      libXi 1.7.8

(wiz)