samples: wifi: ble_coex: Fix possible crash if Zperf fails

In case Zperf session fails (report not received) then the result can be
NULL, add a NULL check.

Signed-off-by: Chaitanya Tata <[email protected]>

Author: krish2718

samples/wifi/ble_coex/src/main.c

@@ -284,6 +284,10 @@ static void udp_upload_results_cb(enum zperf_status status,
 		break;
 	case ZPERF_SESSION_FINISHED:
 		LOG_INF("Wi-Fi benchmark: Upload completed!");
+		if (!result) {
+			LOG_ERR("Result is NULL, Zperf session error");
+			break;
+		}
 		if (result->client_time_in_us != 0U) {
 			client_rate_in_kbps = (uint32_t)
 				(((uint64_t)result->nb_packets_sent *