Make get_mode() easier for static analyzers

Add an explicit check for modes != NULL instead of depending on
num_modes > 0 implying that. This is to silence invalid static analyzer
reports.

Signed-off-by: Jouni Malinen <jouni@codeaurora.org>

wpa_supplicant/wpa_supplicant.c

@@ -8232,6 +8232,9 @@ struct hostapd_hw_modes * get_mode(struct hostapd_hw_modes *modes,
 {
 	u16 i;
 
+	if (!modes)
+		return NULL;
+
 	for (i = 0; i < num_modes; i++) {
 		if (modes[i].mode != mode ||
 		    !modes[i].num_channels || !modes[i].channels)