lossless: simplify HashChainFindCopy heuristics
lossless: simplify HashChainFindCopy heuristics

for small speedup
0.0003 % worse compression

Change-Id: Ic4b6b21e5279231c6321f2cec1c79f7e17e56afa

PKRoma/libwebp,redengineer/libwebp,webmproject/libwebp,ttyangf/libwebp,webmproject/libwebp,PKRoma/libwebp,yohunl/libwebp,redengineer/libwebp,imazen/libwebp,Aexyn/libwebp,Aexyn/libwebp,webmproject/libwebp,webmproject/libwebp,webmproject/libwebp,ttyangf/libwebp,rxl194/libwebp,imazen/libwebp,redengineer/libwebp,imazen/libwebp,Aexyn/libwebp,ttyangf/libwebp,ya7lelkom/libwebp,zofuthan/libwebp,zofuthan/libwebp,yohunl/libwebp,redengineer/libwebp,PKRoma/libwebp,yohunl/libwebp,Aexyn/libwebp,ttyangf/libwebp,rxl194/libwebp,zofuthan/libwebp,redengineer/libwebp,zofuthan/libwebp,ya7lelkom/libwebp,ya7lelkom/libwebp,PKRoma/libwebp,rxl194/libwebp,imazen/libwebp,imazen/libwebp,rxl194/libwebp,PKRoma/libwebp,ya7lelkom/libwebp,yohunl/libwebp,PKRoma/libwebp,Aexyn/libwebp,zofuthan/libwebp,rxl194/libwebp,ya7lelkom/libwebp,yohunl/libwebp,ttyangf/libwebp