#16 Xnn has no effect with low pass filter envelope on

[Arnold Gonzalez]

When the instrument has enabled filter envelope and lowpass filter is selected, Xnn (panning) has no effect - the sample is always played in the center.
Moreover, there are some issues with other filters:
- Bandpass seems to have no influence on sound (or I have hearing problems)
- Highpass, Lowpass2 and Notch do not produce any sound when enabled.
chibitracker 0.9.14.4 compiled under Ubuntu 9.04 AMD
sound driver - Jack