fix: Validate Exchange address_parameters before dereferencing

handle_check_address() read params->address_parameters[0] without
first checking that the pointer was non-NULL or that
address_parameters_length covered at least the length byte. The
function is reachable only from the Exchange app via os_lib_call(),
so this isn't exploitable from a host APDU today, but the contract
between the two libraries lives across a trust boundary and would
silently OOB-read on any future caller that wires up the same
interface less carefully.

Reject params->address_parameters == NULL and
address_parameters_length < 1 early so the function is safe
regardless of who calls it.

(cherry picked from commit c810bc5e759dcd510392eb65f574ee3c3c206679)