FreeImage encoding: also drop down from RGBA to RGB in floating point mode if format doesn't support alpha
FreeImage encoding: also drop down from RGBA to RGB in floating point mode if format doesn't support alpha

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branch : v1-6

digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre,digimatic/ogre