eina: make eina_binbuf_free and eina_strbuff_free accept NULL.
eina: make eina_binbuf_free and eina_strbuff_free accept NULL.

We do follow free() logic here and accept NULL for all eina_*_free() functions.
This patch just do so for Eina_Binbuf and Eina_Strbuf.

Backport from commit 37c1c4e9f662bbb81a11700bd8055d0fbcc933f0
on https://git.enlightenment.org/core/efl.git

gfriloux/eina,gfriloux/eina,gfriloux/eina