st_rados_list_objects.cc: free resources in error case

Fix for:

CID 1251453 (#2 of 2): Resource leak (RESOURCE_LEAK)
 leaked_storage: Variable io_ctx going out of scope leaks the
 storage it points to.

CID 1251454 (#1 of 1): Resource leak (RESOURCE_LEAK)
 leaked_storage: Variable h going out of scope leaks the storage it
 points to.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>