gst/gstclock.c: Make some checks actually useful.

gst/gstclock.c: Make some checks actually useful.

Original commit message from CVS:
* gst/gstclock.c: (gst_clock_set_calibration):
Make some checks actually useful.
* gst/gstregistrybinary.c: (gst_registry_binary_load_plugin):
Remove some unused code. Unsigned integers tend to be >= 0.