Bugfix
   * Fix a null pointer dereference when performing some operations on zero
     represented with 0 limbs: mbedtls_mpi_mod_int() dividing by 2, or
     mbedtls_mpi_write_string() in base 2.

Bugfix
   * Fix a null pointer dereference when performing some operations on zero
     represented with 0 limbs (specifically mbedtls_mpi_mod_int() dividing
     by 2, and mbedtls_mpi_write_string() in base 2).

Clarify potential ambiguity in changelog entry
Clarify potential ambiguity in changelog entry

Signed-off-by: Gilles Peskine <f805f64266d288fc5467baa7be6cd0ff366f477b@arm.com>
