Fix failure when email quota checking is enabled
Fix failure when email quota checking is enabled

This fixes an exception that is raised when EMAIL_BOTO_CHECK_QUOTA is
set to True.

Connects #621

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