Cute quip.
The file contained 1,048,576 bytes (of text) and no newlines. Had that file contained 1,048,575 or 1,048,577 bytes, TCC would not have crashed and would have correctly returned 0.
That also goes for any file with no newlines whose size is exactly a power of two greater than 65536 ... crash ... one more or one fewer character ... no crash.
That certainly is peculiar.