A small typo makes skipping behave incorrectly and in the worst case scenario
leads to an infinite recursion:

        public long skip(long n) throws IOException {
            if (n <= 0) {
                return 0;
            }
            int skipped = 0;
            if (peekb >= 0) {
                peekb = -1;
                skipped++;
                n--;
            }
            return skipped + skip(n);
        }

The last line should have been like this:

            return skipped + in.skip(n);

The method doesn't seem to be used by its enclosing classes. I also haven't
found any evidence an instance of PeekInputStream can escape. Nevertheless I
believe this typo should be fixed.