OWE: Clean up pointer check in a testing code path

Check wpa_auth_write_assoc_resp_owe() return value to keep static
analyzers happier. The code path where this could happen is not really
reachable due to the separate hapd->conf->own_ie_override check and
wpa_auth_write_assoc_resp_owe() returning NULL only in an error case in
the override path. Furthermore, clean up the pointer return value to use
a proper pointer (NULL vs. 0).

Signed-off-by: Ashok Ponnaiah <aponnaia@codeaurora.org>

src/ap/ieee802_11.c

@@ -3021,7 +3021,7 @@ u8 * owe_assoc_req_process(struct hostapd_data *hapd, struct sta_info *sta,
 	owe_buf = wpa_auth_write_assoc_resp_owe(sta->wpa_sm, owe_buf,
 						owe_buf_len, NULL, 0);
 
-	if (sta->owe_ecdh) {
+	if (sta->owe_ecdh && owe_buf) {
 		struct wpabuf *pub;
 
 		pub = crypto_ecdh_get_pubkey(sta->owe_ecdh, 0);

src/ap/wpa_auth_ie.c

@@ -1042,7 +1042,7 @@ u8 * wpa_auth_write_assoc_resp_owe(struct wpa_state_machine *sm,
 #ifdef CONFIG_TESTING_OPTIONS
 	if (conf->own_ie_override_len) {
 		if (max_len < conf->own_ie_override_len)
-			return 0;
+			return NULL;
 		wpa_hexdump(MSG_DEBUG, "WPA: Forced own IE(s) for testing",
 			    conf->own_ie_override, conf->own_ie_override_len);
 		os_memcpy(pos, conf->own_ie_override,