mac80211: Check rate->idx before rate->count

The drivers are not required to fill in rate->count if rate->idx is set
to -1. Hence, we should first check rate->idx before accessing
rate->count.
Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/rc80211_minstrel_ht.c

@@ -300,10 +300,10 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
 static bool
 minstrel_ht_txstat_valid(struct ieee80211_tx_rate *rate)
 {
-	if (!rate->count)
+	if (rate->idx < 0)
 		return false;
 
-	if (rate->idx < 0)
+	if (!rate->count)
 		return false;
 
 	return !!(rate->flags & IEEE80211_TX_RC_MCS);