- Fixed forward stream seeking emulation in streams that don't support seeking

- Fixed forward stream seeking emulation in streams that don't support seeking
  in situations where the read operation gives back less data than requested
  and when there was data in the buffer before the emulation started. Also made
  more consistent its behavior -- should return failure every time less data
  than was requested was skipped.
- Small performance improvement by correcting off-by-one error that generate an
  invalid call to the seek handler or read handler. in _php_stream_seek.