pitch: Fix single input buffer followed by EOS

The flush function immediately returned when pitch->next_buffer_offset
was 0.

This is clearly wrong, as next_buffer_offset can be 0 when a single
input buffer has been received, and no output buffer has been produced
before receiving EOS.

Simply remove that condition.

https://bugzilla.gnome.org/show_bug.cgi?id=796603
1 file changed