libblkid: Fix crash while parsing config with libeconf

libblkid: Fix crash while parsing config with libeconf

As the whole econf_file structure is freed by econf_free(file) at the end
of blkid_read_config(), econf_file structure cannot be defined as static
and initialized only once. The econf_free() is not robust enough and keeps
a pointer to the garbage after the first call of blkid_read_config(). And
if /etc/blkid.conf does not exist, it is called second time.

Signed-off-by: Stanislav Brabec <sbrabec@suse.cz>
Cc: Stefan Schubert <schubi@suse.de>
Link: https://bugzilla.opensuse.org/show_bug.cgi?id=1242705
(cherry picked from commit 284527cff2bd22da2924881a4a4833049dca0d2e)