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/ucs1lib.h b/Objects/stringlib/ucs1lib.h
index c0f7adf..0b82a84 100644
--- a/Objects/stringlib/ucs1lib.h
+++ b/Objects/stringlib/ucs1lib.h
@@ -6,6 +6,7 @@
 #define FASTSEARCH               ucs1lib_fastsearch
 #define STRINGLIB(F)             ucs1lib_##F
 #define STRINGLIB_OBJECT         PyUnicodeObject
+#define STRINGLIB_SIZEOF_CHAR    1
 #define STRINGLIB_CHAR           Py_UCS1
 #define STRINGLIB_TYPE_NAME      "unicode"
 #define STRINGLIB_PARSE_CODE     "U"