fix: buffer slice last byte out of range

[3l0w]

Problem description

Fixes: #1880
The slice buffer node 'to' variable cannot be set to capture the last byte, throwing 'to' input out of range.

Implementation description

The upper bound check was an greater or equals than, so switching it to a greater than fixes the issue.

[paxcut]

I guess we have two choices. We can use C-like indices of 0..N-1 to slice N elements. ImHex uses an iterator like system where 0..N selects the first N elements so that the end number is one past the end of the buffer.
The fix proposed here follows ImHex's model.To implement a C like index system use:

this->setBufferOnOutput(3, std::vector(input.begin() + u64(from), input.begin() + u64(to + 1)));

and leave the error condition for to as it was.

I think either one is fine but I wanted to make sure that the choice is deliberate and not accidental due to the bug.