AnimEncoder API: GenerateCandidates bugfix.
AnimEncoder API: GenerateCandidates bugfix.

As 'curr_canvas_mod' is being modified during calls to IncreaseTransparency()
and FlattenSimilarBlocks(), GetSubRect() should get the sub-frame from
'curr_canvas_mod' as well.

Earlier, GetSubRect() was computed from 'curr_canvas', so modifying
'curr_canvas_mod' had no effect on encoding.

Change-Id: Ia847503007b66364817fe57def5a9e3c37d1b3cc

jacklicn/libwebp,kim42083/webm.libwebp,Suvarna1488/webm.libwebp,jiehu5114/libwebp,PKRoma/libwebp,kim42083/webm.libwebp,zofuthan/libwebp,Acidburn0zzz/webm.libwebp,PKRoma/libwebp,reimaginemedia/webm.libwebp,Maria1099/webm.libwebp,kalli123/webm.libwebp,altogother/webm.libwebp,webmproject/libwebp,PKRoma/libwebp,rxl194/libwebp,kalli123/webm.libwebp,yohunl/libwebp,jacklicn/libwebp,redengineer/libwebp,ya7lelkom/libwebp,ericmckean/webm.libwebp,zofuthan/libwebp,Acidburn0zzz/webm.libwebp,Aexyn/libwebp,kleopatra999/webm.libwebp,gshORTON/webm.libwebp,kleopatra999/webm.libwebp,webmproject/libwebp,imazen/libwebp,PKRoma/libwebp,PKRoma/libwebp,yohunl/libwebp,yohunl/libwebp,altogother/webm.libwebp,Suvarna1488/webm.libwebp,kalli123/webm.libwebp,iniwf/webm.libwebp,matanbs/webm.libwebp,ya7lelkom/libwebp,kim42083/webm.libwebp,Aexyn/libwebp,rxl194/libwebp,yohunl/libwebp,rxl194/libwebp,Aexyn/libwebp,imazen/libwebp,iniwf/webm.libwebp,abwiz0086/webm.libwebp,Acidburn0zzz/webm.libwebp,ttyangf/libwebp,webmproject/libwebp,abwiz0086/webm.libwebp,Aexyn/libwebp,jiehu5114/libwebp,ttyangf/libwebp,imazen/libwebp,reimaginemedia/webm.libwebp,imazen/libwebp,jiehu5114/libwebp,gshORTON/webm.libwebp,Maria1099/webm.libwebp,yohunl/libwebp,Suvarna1488/webm.libwebp,altogother/webm.libwebp,webmproject/libwebp,imazen/libwebp,ttyangf/libwebp,rxl194/libwebp,kim42083/webm.libwebp,iniwf/webm.libwebp,zofuthan/libwebp,Aexyn/libwebp,gshORTON/webm.libwebp,ttyangf/libwebp,iniwf/webm.libwebp,PKRoma/libwebp,ya7lelkom/libwebp,kalli123/webm.libwebp,abwiz0086/webm.libwebp,ya7lelkom/libwebp,Maria1099/webm.libwebp,Maria1099/webm.libwebp,Acidburn0zzz/webm.libwebp,reimaginemedia/webm.libwebp,jacklicn/libwebp,jiehu5114/libwebp,matanbs/webm.libwebp,kim42083/webm.libwebp,Acidburn0zzz/webm.libwebp,ericmckean/webm.libwebp,gshORTON/webm.libwebp,reimaginemedia/webm.libwebp,zofuthan/libwebp,kleopatra999/webm.libwebp,jacklicn/libwebp,matanbs/webm.libwebp,kleopatra999/webm.libwebp,redengineer/libwebp,ttyangf/libwebp,matanbs/webm.libwebp,abwiz0086/webm.libwebp,matanbs/webm.libwebp,gshORTON/webm.libwebp,altogother/webm.libwebp,webmproject/libwebp,redengineer/libwebp,abwiz0086/webm.libwebp,ericmckean/webm.libwebp,Suvarna1488/webm.libwebp,Maria1099/webm.libwebp,ericmckean/webm.libwebp,kalli123/webm.libwebp,kleopatra999/webm.libwebp,jiehu5114/libwebp,redengineer/libwebp,reimaginemedia/webm.libwebp,rxl194/libwebp,iniwf/webm.libwebp,Suvarna1488/webm.libwebp,ericmckean/webm.libwebp,ya7lelkom/libwebp,jacklicn/libwebp,zofuthan/libwebp,redengineer/libwebp,altogother/webm.libwebp