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.

src/lib/eina/eina_binbuf_template_c.x

@@ -77,6 +77,8 @@ _FUNC_EXPAND(manage_new_length)(_STRBUF_DATA_TYPE *str, size_t length)
 EAPI void
 _FUNC_EXPAND(free)(_STRBUF_STRUCT_NAME *buf)
 {
+   if (!buf) return ;
+
    EINA_MAGIC_CHECK_STRBUF(buf);
    EINA_MAGIC_SET(buf, EINA_MAGIC_NONE);
    eina_strbuf_common_free(buf);