Attempt to workaround problem reported about empty plc.xml after unrelated crash. Now, if etree model is corrupted in a way tostring() would generate an empty string, exception prevents saving.

[main]
host = https://www.transifex.com

[beremiz-ide.beremiz]
file_filter = Beremiz_<lang>.po
minimum_perc = 0
source_file = messages.pot
source_lang = en
type = PO