HO: fix minor issues found by coverity

handover_decision_2:
- lchan->conn should never be NULL, but if it is, don't crash in LOGPHO*
  macros.
- make certain to avoid modulo-zero. It's cosmetic since that config item is
  not allowed to be zero.

handover_test:
- check return value of gsm_generate_si().
- safer evaluation of main()'s argv.

Fixes: CID#182929, CID#182928, CID#182927, CID#182926
Change-Id: I68e8ed3a1e8659edb47ac3e8a10508f17a3f5670
2 files changed