gtk_curve_set_curve_type() will generally result in a call
to gtk_curve_interpolate(). neither function checks to see if the widget
has been sized yet. as a result, if gtk_curve_set_type() is called during
widget initialization, the call to gtk_curve_interpolate() finds itself
using a width of -1. This leads the following call:

          g_malloc (width * sizeof (foo))

to attempt to allocate -20 bytes, which aborts the program.

the documentation for gtk_curve_set_type() should either indicate
that it cannot be called till the curve has been realized, or better,
the functions should check on the current status of the widget and
act accordingly.