Config: If cf_def_file is NULL, initialize the configuration.

Config: If cf_def_file is NULL, initialize the configuration.

Otherwise we end up uninitialized clists and other nasty stuff. (The problems
were rarely visible, but the recent changes to conf-input.c have caused some
extra commits, which crashed when no configuration was loaded.)

This is a departure from the behavior of LibUCW 3.12, but I think we should
guarantee that after cf_getopt(), the configuration is always in a consistent
state, meaning that it has been initialized and committed. This should not
depend on whether the default config file was loaded or not.

On the other hand, program which avoid cf_getopt() and call cf_load() are on
their own, there is no implicit commit for them yet. Maybe this should be
fixed, too.