hex: make wraparound of the index into ring-buffer explicit
Overflow is defined for unsigned integers, but not for signed ones.
We could make the ring-buffer index in sha1_to_hex() and
get_pathname() unsigned to be on the safe side to resolve this, but
let's make it explicit that we are wrapping around at whatever the
number of elements the ring-buffer has. The compiler is smart enough
to turn modulus into bitmask for these codepaths that use
ring-buffers of a size that is a power of 2.
Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>