A risk of writing to an invalid address with memcpy in function Parser_feed

Parser_feed(Parser* self, PyObject *args)
{
     ........
     if((size_t)data_len > self->buffer_capacity - (self->buffer_end - self->buffer_start)) {
            self->buffer_capacity = MAX(self->buffer_capacity * 2, self->buffer_end - self->buffer_start + data_len);
            if(self->buffer == self->inline_buffer) {
                   self->buffer = malloc(self->buffer_capacity);    --------> may return a NULL pointer
                   memcpy(self->buffer + self->buffer_start, self->inline_buffer + self->buffer_start,
                                  self->buffer_end - self->buffer_start);
    } 
    ........
}