Integer overflow in SequentialStreamReader causes wrong length check

[KirkLandTrip]

I have a corrupt image which goes into an infinite loop when running Metadata Extractor on it.
Some of the bad code is on my end (bad implementation of Stream) but one of the fail points is also in Metadata Extractor.

In the SequentialStreamReader class, The Skip method does a bounds check on position + n > length:

In my case, n (num bytes to skip) was very large but still positive (top-most bit is off) 0x7fffffffffffffef = 9223372036854775791
and the addition of position + n lit the top-most bit, so the result is a negative long 0x8000000000014b86 = -9223372036854690938

Since both sides of the comparison are long and -9223372036854690938 < 131072 then the bounds violation is not detected.

I made a PR to fix this issue: simply casting both sides of the comparison to ulong should solve it:
#427

I hope this helps.