libsepol: do not seg fault on sepol_*_key_free(NULL)

sepol_*_key_free(NULL) should just be a no-op just like
free(NULL).  Fix several instances that did not handle this
correctly and would seg fault if called with NULL.

Test: setsebool -P zebra_write_config=1 while non-root

Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
3 files changed