hash: better handling of NULL, add magic checking.

hash: better handling of NULL, add magic checking.

 * evas: if we automatically destroy hash, check for NULL before
   handling it to eina api, which expect elements to be created with
   eina_hash_new() and thus will fail on NULL.
 * eina: add magic checking for eina_hash and eina_hash_iterator, this will
   help spot when NULL is used.
 * eina_hash_foreach: do not try to create the iterator if hash is NULL.

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/eina@37982 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33