Fix fastsearch for UCS2 and UCS4

 * If needle is 0, try (p[0] >> 16) & 0xff for UCS4
 * Disable fastsearch_memchr_1char() if needle is zero for UCS2 and UCS4
diff --git a/Objects/stringlib/ucs4lib.h b/Objects/stringlib/ucs4lib.h
index be1206a..988ddc0 100644
--- a/Objects/stringlib/ucs4lib.h
+++ b/Objects/stringlib/ucs4lib.h
@@ -6,6 +6,7 @@
 #define FASTSEARCH               ucs4lib_fastsearch
 #define STRINGLIB(F)             ucs4lib_##F
 #define STRINGLIB_OBJECT         PyUnicodeObject
+#define STRINGLIB_SIZEOF_CHAR    4
 #define STRINGLIB_CHAR           Py_UCS4
 #define STRINGLIB_TYPE_NAME      "unicode"
 #define STRINGLIB_PARSE_CODE     "U"