libmsc/ran_msg_a.c: prevent chosen_encryption->key buffer overrun

In ran_a_make_handover_request() we do prevent destination buffer
(r.encryption_information.key) overflow, but not source buffer
(n->geran.chosen_encryption->key) overrun if an incorrect key
length is received. Let's fix this.

Change-Id: I278bb72660634c2d535e1bd3d7fce5696da23575
Fixes: CID#198450 Out-of-bounds access
1 file changed