XYGraph__ClearPlot (ul_pbar_graphics)

 *  Synopsis:
 *    #include <ul_pbar_graphics:xygraph.h>
 *
 *    TXYGraph__Result XYGraph__ClearPlot( void )
 *
 *  Function intent:
 *    XYGraph__ClearPlot() clears the entire plot area of the X-Y graph display
 *    and redraws the axis and grid.
 *  Function parameters:
 *    none
 *  Function return value:
 *    CBS_OK		success
 *    CBS_NOSETUP	XYGraph__DisplayGraph() has not been called
 *    else 		wn_xxx() function error occured