Fix error when cancelling single blockface
Fix error when cancelling single blockface

Fixes #681
Fixes #1230

kdeloach/nyc-trees,azavea/nyc-trees,maurizi/nyc-trees,kdeloach/nyc-trees,azavea/nyc-trees,kdeloach/nyc-trees,kdeloach/nyc-trees,azavea/nyc-trees,maurizi/nyc-trees,maurizi/nyc-trees,kdeloach/nyc-trees,maurizi/nyc-trees,azavea/nyc-trees,azavea/nyc-trees