Fixed memory leak in CPGraph.
Fixed memory leak in CPGraph.

tectronics/core-plot,sureshdustrise/core-plot,divyavamsee/core-plot,LiDechao/core-plot,celery01/celery01-drawing-plot,tectronics/core-plot,kamalvenkat/core-plot,eoinnorris/core-plot,kamalvenkat/core-plot,eoinnorris/core-plot,celery01/celery01-drawing-plot,sureshdustrise/core-plot,LiDechao/core-plot,zenXian/core-plot,celery01/celery01-drawing-plot,sureshdustrise/core-plot,zenXian/core-plot,kamalvenkat/core-plot,eoinnorris/core-plot,tectronics/core-plot,tectronics/core-plot,celery01/celery01-drawing-plot,divyavamsee/core-plot,LiDechao/core-plot,zenXian/core-plot,sureshdustrise/core-plot,zenXian/core-plot,kamalvenkat/core-plot,eoinnorris/core-plot,divyavamsee/core-plot,LiDechao/core-plot,divyavamsee/core-plot,celery01/celery01-drawing-plot