Give better error msg when xml config file is invalid.

Especially since config file format changed.

passing the old format (that most tutorials on ezstream use) gives a not really useful remark (not even error):

<ezstream>
    <url>http://localhost:8000/goodmusic</url>
    <sourcepassword>make-up-your-own</sourcepassword>
    <format>MP3</format>
    <filename>/mnt/music/goodmusic/playlist.m3u</filename>
    <shuffle>1</shuffle>
    <stream_once>0</stream_once>
    <svrinfoname>Good Music</svrinfoname>
    <svrinfourl>pihole.local</svrinfourl>
    <svrinfogenre>Good Music Streaming 24x7</svrinfogenre>
    <svrinfodescription>Techno Dub</svrinfodescription>
    <svrinfobitrate>128</svrinfobitrate>
    <svrinfochannels>2</svrinfochannels>
    <svrinfosamplerate>44100</svrinfosamplerate>
    <svrinfopublic>1</svrinfopublic>
</ezstream>

~$   ezstream -c test.xml
ezstream[313100]: test.xml: world readable
ezstream[313100]: stream: default: no configuration

No idea what to do next, wasted half a day on this.