[nrf noup] zephyr: Print only non-null buffers

fixup! [nrf noup] zephyr: Add support for WPA CLI zephyr

Print only non-empty responses.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>

wpa_supplicant/wpa_cli_zephyr.c

@@ -76,7 +76,8 @@ static int _wpa_ctrl_command(struct wpa_ctrl *ctrl, const char *cmd, int print,
 
 	if (print) {
 			buf[len] = '\0';
-			printf("%s", buf);
+			if (buf)
+				printf("%s", buf);
 	}
 	return 0;
 }