libcgroup: Added checks for NULL when creating an internal dictionary
libcgroup: Added checks for NULL when creating an internal dictionary

Added one check for null when creating an internal dictionary
and fixed checking of calloc result.

Changelog:
  - rephrased the commit message

Signed-off-by: Jan Safranek <a7f4b96ffdd515ecef00f117294da18555749b0b@redhat.com>

jrfastab/Linux-cgdcbxd,rafalmiel/libcg,rafalmiel/libcg,jrfastab/Linux-cgdcbxd,jrfastab/Linux-cgdcbxd,rafalmiel/libcg,rafalmiel/libcg,jrfastab/Linux-cgdcbxd