Fix an error case in krb5_sendauth

If we fail to get the client principal when constructing the
stack-allocated creds structure, don't double-free creds.server.
Fix an error case in krb5int_fcc_new_unique

If we fail to allocate setptr, don't close ret, since we've already
done so.
Fix unused assignment in mechglue loadConfigFile
Init output parameter of krb5_decode_princ_entry

For easier static analysis, make sure that krb5_decode_princ_entry
always sets *entry_ptr to a valid entry or NULL.