Bugfix: tone generator input and seeks beyond stream end
Bugfix: tone generator input and seeks beyond stream end

If a tone generator input was set to have fixed lenght,
and then a seek is perform beyond end-of-stream, that would
cause a segfault.

jeremysalwen/Ecasound-LV2,jeremysalwen/Ecasound-LV2,jeremysalwen/Ecasound-LV2,jeremysalwen/Ecasound-LV2,jeremysalwen/Ecasound-LV2