Fix segfault when libibverbs returns 0 device. (#1820)

Fix: SWDEV-543816

src/misc/ibvwrap.cc

@@ -107,6 +107,7 @@ ncclResult_t wrap_ibv_get_device_list(struct ibv_device ***ret, int *num_devices
 }
 
 ncclResult_t wrap_ibv_free_device_list(struct ibv_device **list) {
+  if (list == nullptr) return ncclSuccess;
   IBV_PASSTHRU(ibvSymbols, ibv_internal_free_device_list, ibv_internal_free_device_list(list));
 }