Make sure unused parts of tag buffer are cleared
Make sure unused parts of tag buffer are cleared

We already did this on failure, but make sure the buffer does not leak
what was in it previously on success

Signed-off-by: Paul Elliott <c95151bd40fac1aa138ed1651e2873f91d2e1899@arm.com>

NXPmicro/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls