added guards to marking slice as failed (#422)
added guards to marking slice as failed (#422)


jsnoble/teraslice,terascope/teraslice,terascope/teraslice,godber/teraslice,jsnoble/teraslice,jsnoble/teraslice,jsnoble/teraslice,terascope/teraslice,terascope/teraslice,jsnoble/teraslice,godber/teraslice,godber/teraslice