Avoid crash during config directory migration

Do not call Log_Print() during early application startup, to avoid the
situation before EtApplicationWindow and EtLogArea have been
instantiated where logging a message will fail.

https://retrace.fedoraproject.org/faf2/problems/552599/
Remove broken early logging code

The code to store a temporary list for logging messages during early
application startup was broken, and needs to be rethought.
Add an invariant in Log_Print()

Return and log a critical message if EtLogArea has not been initialized
when calling Log_Print().