fix conversion warning on MSVC
fix conversion warning on MSVC

"src\enc\frame.c(88) : warning C4244: '=' : conversion from 'const double' to 'float', possible loss of data"

Change-Id: I143cb0bb6b69e1b8befe9b4f24b71adbc28095c2

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