Revision 1777374

PDFBOX-3000, PDFBOX-3564: new softmask handling with bounds, by John Hewson and Petr Slaby;
use the colormodel corresponding to the source raster to convert into the components, as suggested by Matthias Blaesing; 
avoid ArrayIndexOutOfBoundsException, simplify output raster creation, assign rgba[3] only if within bounds;use /bc color in softmask outside bounds