fix VC12-x64 warning
fix VC12-x64 warning

"conversion from 'vp8l_atype_t' to 'uint8_t', possible loss of data"

Change-Id: I7607a688d16aca8fae8ce472450f8423c48f3a26

Suvarna1488/webm.libwebp,Aexyn/libwebp,Acidburn0zzz/webm.libwebp,iniwf/webm.libwebp,altogother/webm.libwebp,imazen/libwebp,PKRoma/libwebp,reimaginemedia/webm.libwebp,appunite/libwebp,Maria1099/webm.libwebp,keane83/BLE_IM,altogother/webm.libwebp,kleopatra999/webm.libwebp,redengineer/libwebp,Aexyn/libwebp,kalli123/webm.libwebp,comoyo/gonzo-libwebp,gshORTON/webm.libwebp,jiehu5114/libwebp,appunite/libwebp,ttyangf/libwebp,abwiz0086/webm.libwebp,keane83/BLE_IM,matanbs/webm.libwebp,jiehu5114/libwebp,reimaginemedia/webm.libwebp,iniwf/webm.libwebp,Acidburn0zzz/webm.libwebp,webmproject/libwebp,jiehu5114/libwebp,comoyo/gonzo-libwebp,ya7lelkom/libwebp,keane83/BLE_IM,kleopatra999/webm.libwebp,appunite/libwebp,PKRoma/libwebp,rxl194/libwebp,ya7lelkom/libwebp,Suvarna1488/webm.libwebp,yohunl/libwebp,rxl194/libwebp,ttyangf/libwebp,Suvarna1488/webm.libwebp,redengineer/libwebp,zofuthan/libwebp,ericmckean/webm.libwebp,abwiz0086/webm.libwebp,webmproject/libwebp,Aexyn/libwebp,comoyo/gonzo-libwebp,Maria1099/webm.libwebp,Maria1099/webm.libwebp,yohunl/libwebp,Aexyn/libwebp,comoyo/gonzo-libwebp,yohunl/libwebp,ttyangf/libwebp,webmproject/libwebp,redengineer/libwebp,abwiz0086/webm.libwebp,kalli123/webm.libwebp,Maria1099/webm.libwebp,Acidburn0zzz/webm.libwebp,Acidburn0zzz/webm.libwebp,zofuthan/libwebp,kim42083/webm.libwebp,comoyo/gonzo-libwebp,Suvarna1488/webm.libwebp,rxl194/libwebp,ya7lelkom/libwebp,jacklicn/libwebp,abwiz0086/webm.libwebp,Maria1099/webm.libwebp,keane83/BLE_IM,kleopatra999/webm.libwebp,appunite/libwebp,gshORTON/webm.libwebp,zofuthan/libwebp,ericmckean/webm.libwebp,reimaginemedia/webm.libwebp,rxl194/libwebp,kim42083/webm.libwebp,Aexyn/libwebp,kleopatra999/webm.libwebp,ya7lelkom/libwebp,zofuthan/libwebp,imazen/libwebp,Suvarna1488/webm.libwebp,ericmckean/webm.libwebp,matanbs/webm.libwebp,matanbs/webm.libwebp,ericmckean/webm.libwebp,kim42083/webm.libwebp,gshORTON/webm.libwebp,iniwf/webm.libwebp,kalli123/webm.libwebp,kleopatra999/webm.libwebp,iniwf/webm.libwebp,kim42083/webm.libwebp,ya7lelkom/libwebp,rxl194/libwebp,zofuthan/libwebp,yohunl/libwebp,reimaginemedia/webm.libwebp,imazen/libwebp,gshORTON/webm.libwebp,redengineer/libwebp,appunite/libwebp,yohunl/libwebp,PKRoma/libwebp,ttyangf/libwebp,keane83/BLE_IM,altogother/webm.libwebp,comoyo/gonzo-libwebp,kalli123/webm.libwebp,altogother/webm.libwebp,webmproject/libwebp,PKRoma/libwebp,altogother/webm.libwebp,comoyo/gonzo-libwebp,ericmckean/webm.libwebp,jiehu5114/libwebp,kalli123/webm.libwebp,reimaginemedia/webm.libwebp,jiehu5114/libwebp,jacklicn/libwebp,Acidburn0zzz/webm.libwebp,imazen/libwebp,PKRoma/libwebp,jacklicn/libwebp,matanbs/webm.libwebp,imazen/libwebp,PKRoma/libwebp,iniwf/webm.libwebp,abwiz0086/webm.libwebp,appunite/libwebp,redengineer/libwebp,jacklicn/libwebp,jacklicn/libwebp,ttyangf/libwebp,kim42083/webm.libwebp,webmproject/libwebp,gshORTON/webm.libwebp,matanbs/webm.libwebp