dns_baidu, dns_bhosted: pipe input to _lower_case, not an argument

_lower_case reads stdin only. Called as _lower_case "$x", the argument
was dropped and tr read the inherited stdin. On an interactive tty that
never reaches EOF, so dns_baidu hung forever on every add/rm (#7319).
Under cron stdin is /dev/null and the value came back empty: dns_baidu
fell into the default engine order by luck, and the dns_bhosted
fallback error checks could never match.

Fixes #7319

dnsapi/dns_baidu.sh

@@ -120,7 +120,7 @@ _baidu_run_with_fallback() {
 }
 
 _baidu_engine_order() {
-  _pref="$(_lower_case "$(_baidu_trim_ws "${Baidu_API_Preference:-auto}")")"
+  _pref="$(_baidu_trim_ws "${Baidu_API_Preference:-auto}" | _lower_case)"
   case "$_pref" in
   legacy)
     printf "%s" "legacy new"