runqueue: validate_hashes(): currentcount should be a number

runqueue: validate_hashes(): currentcount should be a number

According to sstate_checkhashes which is defined in sstate.bbclass, the
currentcoun should be a number (0, not None).

Fixed:
$ bitbake base-files -Sprintdiff
    >    bb.plain("Sstate summary: Wanted %d Found %d Missed %d Current %d (%d%% match, %d%% complete)" % (total, len(found), len(missed), currentcount, match, complete))

TypeError: %d format: a number is required, not NoneType

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>