When is '//' removed we access i + 2 indecies. But array is 257 length and iterate until 256, on last iteration 255 + 2 == 257 and we out-of-bounds.

There:

https://github.com/bitcoin/bitcoin/blob/master/src/qt/qtipcserver.cpp#L37
https://github.com/bitcoin/bitcoin/blob/master/src/qt/qtipcserver.cpp#L73