fix stroke color set despite none
fix stroke color set despite none

bloomberg/bqplot,ChakriCherukuri/bqplot,ChakriCherukuri/bqplot,bloomberg/bqplot,SylvainCorlay/bqplot,ChakriCherukuri/bqplot,SylvainCorlay/bqplot,bloomberg/bqplot,SylvainCorlay/bqplot