t is never used uninitialized, since the first loop iteration reads 0
bytes of it and then writes hash_len bytes, and subsequent iterations
read and write hash_len bytes. However this is somewhat fragile, and
it would be legitimate for a static analyzer to be unsure.
Initialize t explicitly, to make the code clearer and more robust, at
negligible cost.
Reported by Vasily Evseenko in
https://github.com/ARMmbed/mbedtls/pull/2942
with a slightly different fix.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
