Exit on data directory creation error

No point in creating (sub)directories when the given root failed already
as is the case when e.g. XDG_DATA_HOME/catgirl/ itself is bogus
(cleaned stderr intermangled with ncurses setup/catgirl output):

	$ env -i TERM=xterm XDG_DATA_HOME=/ ./catgirl -h irc.hackint.eu -n nobody -l
	catgirl: //catgirl/: Permission denied
	catgirl: //catgirl/log: No such file or directory
	catgirl: //catgirl/log/hackint: No such file or directory
	catgirl: //catgirl/log/hackint/NickServ: No such file or directory
	catgirl: //catgirl/: Permission denied
	catgirl: //catgirl/log/hackint/NickServ/2021-06-13.log: No such file or directory

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