Make calculateBlackAreas() publicly available.
Make calculateBlackAreas() publicly available.

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