Description:
------------
Sometimes if the key has the "\0"-character within caching storing or reading of this item fails.

Reproduce code:
---------------
apc_store("\0", "test1");
var_dump(apc_exists("\0"));
var_dump(apc_fetch("\0"));

apc_store("-\0-", "test2");
var_dump(apc_exists("-\0-"));
var_dump(apc_fetch("-\0-"));

apc_store("-\1-", "test3");
var_dump(apc_exists("-\1-"));
var_dump(apc_fetch("-\1-"));

Expected result:
----------------
bool(true)
string(5) "test1"
bool(true)
string(5) "test2"
bool(true)
string(5) "test3"

Actual result:
--------------
bool(true)
string(5) "test1"
NULL
bool(false)
bool(true)
string(5) "test3"