libFLAC: fix more problems with new window functions
libFLAC: fix more problems with new window functions

This fixes two problems with handling of out-of-bounds arguments
for the window functions, one of which involving an infinite loop

Signed-off-by: Erik de Castro Lopo <1586a8e151fb6d548e7a343b9bcdfea42e83ffc0@mega-nerd.com>

waitman/flac,waitman/flac,waitman/flac,waitman/flac,waitman/flac