qcacld-3.0: Fix invalid access in vendor cmd handler

While processing vendor command: GET_PREFERRED_FREQ_LIST respective
handler __wlan_hdd_cfg80211_get_preferred_freq_list() do not validate
pcl_len received from policy_mgr_get_pcl() which can be zero when
current regulatory domain is ETSI13 based, gindoor_channel_support=0
and etsi13_srd_chan_in_master_mode=0.

If pcl_len is zero then invalid index is computed in
wlan_hdd_populate_weigh_pcl() when trying to access
chan_weights->weight_list[pcl_len - 1].

To fix this, add zero length check for pcl_len before accessing
weight_list[plc_len - 1].

Change-Id: Ie8bf52fe289634efc104ca674d70fcd1beb6c304
CRs-Fixed: 2492630

core/hdd/src/wlan_hdd_cfg80211.c

@@ -8434,7 +8434,7 @@ static uint32_t wlan_hdd_populate_weigh_pcl(
 			w_pcl[i].flag = set | PCL_CHANNEL_SUPPORT_CLI;
 	}
 	chan_idx = pcl_len;
-	if (chan_weights->weight_list[pcl_len - 1] >
+	if (pcl_len && chan_weights->weight_list[pcl_len - 1] >
 	    PCL_GROUPS_WEIGHT_DIFFERENCE)
 	/* Set non-pcl channels weight 20 point less than the last PCL entry */
 		valid_weight = chan_weights->weight_list[pcl_len - 1] -