AnimEncoder API: Compute change rectangle for first frame too.
AnimEncoder API: Compute change rectangle for first frame too.

Earlier, we were always using full canvas for first frame.

Change-Id: Ib8d32961682c4b07010ea559a71dd59ab9ec0157

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