fix: reject None data in tp_init, matching hashlib

Remove data_obj != Py_None check so None triggers _get_buffer_or_str
which raises TypeError via PyObject_GetBuffer, consistent with
hashlib.md5(None) behavior.

Author: ifduyue

src/_xxhash.c

@@ -529,7 +529,7 @@ static int PYXXH32_init(PYXXH32Object *self, PyObject *args, PyObject *kwargs)
         return -1;
     }
 
-    if (data_obj && data_obj != Py_None) {
+    if (data_obj) {
             if (_get_buffer_or_str(data_obj, &buf) < 0)
             return -1;
         }
@@ -884,7 +884,7 @@ static int PYXXH64_init(PYXXH64Object *self, PyObject *args, PyObject *kwargs)
         return -1;
     }
 
-    if (data_obj && data_obj != Py_None) {
+    if (data_obj) {
             if (_get_buffer_or_str(data_obj, &buf) < 0)
             return -1;
         }
@@ -1238,7 +1238,7 @@ static int PYXXH3_64_init(PYXXH3_64Object *self, PyObject *args, PyObject *kwarg
         return -1;
     }
 
-    if (data_obj && data_obj != Py_None) {
+    if (data_obj) {
             if (_get_buffer_or_str(data_obj, &buf) < 0)
             return -1;
         }
@@ -1601,7 +1601,7 @@ static int PYXXH3_128_init(PYXXH3_128Object *self, PyObject *args, PyObject *kwa
         return -1;
     }
 
-    if (data_obj && data_obj != Py_None) {
+    if (data_obj) {
             if (_get_buffer_or_str(data_obj, &buf) < 0)
             return -1;
         }