gst/: Don't put functional code in g_return_if_fail() or g_return_val_if_fail() statements, otherwise things will bre...

Original commit message from CVS:
* gst/base/gstbasetransform.c: (gst_base_transform_transform_size):
* gst/gstutils.c: (gst_util_set_value_from_string),
(gst_util_set_object_arg):
Don't put functional code in g_return_if_fail() or
g_return_val_if_fail() statements, otherwise things will
break when G_DISABLE_CHECKS is defined during compilation.