Fix MYSQL_TYPE_NULL data pointer advancement in call_function_rowdat_1

The MYSQL_TYPE_NULL case in call_function_rowdat_1 was missing the
`data += 1` advancement after reading the null flag byte. This caused
data stream desynchronization for all subsequent columns and rows,
leading to data corruption or crashes. The fix aligns with the existing
behavior in load_rowdat_1 and load_rowdat_1_numpy.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kesmit13

accel.c

@@ -4911,6 +4911,7 @@ static PyObject *call_function_accel(PyObject *self, PyObject *args, PyObject *k
 
             switch (ctypes[i]) {
             case MYSQL_TYPE_NULL:
+                data += 1;
                 Py_INCREF(Py_None);
                 CHECKRC(PyTuple_SetItem(py_row, i, Py_None));
                 break;