libs/gst/controller/: Protect against values larger or smaller than the minimum or maximum allowed value for the prop...

Original commit message from CVS:
* libs/gst/controller/gstcontroller.c:
(gst_controlled_property_new):
* libs/gst/controller/gstcontrollerprivate.h:
* libs/gst/controller/gstinterpolation.c:
(gst_controlled_property_find_control_point_node),
(interpolate_none_get), (interpolate_none_get_enum_value_array),
(interpolate_none_get_string_value_array),
(interpolate_trigger_get),
(interpolate_trigger_get_enum_value_array),
(interpolate_trigger_get_string_value_array):
Protect against values larger or smaller than the minimum or maximum
allowed value for the property when using values that can be compared.
Optimize trigger interpolator a bit by taking the last requested value
into account instead of always looping through the complete list.
Fix coding style a bit, everywhere else we use "return foo" instead
of "return (foo)".
* tests/check/libs/controller.c: (GST_START_TEST),
(gst_controller_suite):
Add unit test for the protection against too large or too small
values.