Fix bugs in previous cc_file.c changes

In fcc_destroy and krb5int_fcc_new_unique, call set_errmsg_filename
before deleting the cache handle, or else the reference to
data->filename is a use after free.

In set_errmsg_filename, do nothing if the code is 0, as we don't have
an error to annotate.

https://github.com/krb5/krb5/commit/14f039b40efd91b93b1148765bf0b7d3c90db58a
Author: Greg Hudson <ghudson@mit.edu>
Commit: 14f039b40efd91b93b1148765bf0b7d3c90db58a
Branch: master
 src/lib/krb5/ccache/cc_file.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)