Fix compilation with --disable-everything --enable-demuxer=loas
lavfi/showwaves: fix check on showwaves->outpicref

outpicref is not always in synch with showwaves->outpicref, which is
changed as a side effect of the call to functions.

Fix regression introduced in 5f634480d1c4ed7711a15d1be07e49177cf351c1,
+10l to me.
lagarith: return more meaningful error codes

Signed-off-by: Paul B Mahol <onemda@gmail.com>
sanm: check image dimensions before using them

Avoids integer overflows and out of array accesses.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>