decodeUncompressed(): cast before multiplying
decodeUncompressed(): cast before multiplying

I fixed that in darktable-org/darktable@98a970a97154056cea68cf674869492245f88528, but eventually it was forgot until now...

Coverity CID 1230646

darktable-org/rawspeed,LebedevRI/rawspeed,anarsoul/rawspeed,anarsoul/rawspeed,LebedevRI/rawspeed,klauspost/rawspeed,mgehre/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,anarsoul/rawspeed,LebedevRI/rawspeed,klauspost/rawspeed,mgehre/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed