qcacld-3.0: validate the green_ap_ctx before accessing it

qcacld-2.0 to qcacld-3.0 propagation

The green_ap_ctx is not checked for NULL pointer before accessing
it. This is leading to crash in FTM mode as green_ap_ctx is not
initialized.

CRs-Fixed: 1074982
Change-Id: I6b3cea999bfb44cfb6fa56aece6b423e638bfaa7

core/hdd/src/wlan_hdd_green_ap.c

@@ -399,6 +399,11 @@ void hdd_green_ap_start_bss(struct hdd_context_s *hdd_ctx)
 {
 	struct hdd_config *cfg = hdd_ctx->config;
 
+	if (!hdd_ctx->green_ap_ctx) {
+		hdd_err("Green AP is not enabled. green_ap_ctx = NULL");
+		goto exit;
+	}
+
 	/* check if the firmware and ini are both enabled the egap,
 	 * and also the feature_flag enable, then we enable the egap
 	 */