BUG: Fix error when image or mask is not loaded correctly
BUG: Fix error when image or mask is not loaded correctly

When segmentation is passed as a SimpleITK image, as the second check erroneously checks the imageFilePath instead of the maskFilePath for being an SimpleITK Image.
Addtionally, add some checks to ensure image and mask are loaded before attempting to process further.

Radiomics/pyradiomics,Radiomics/pyradiomics,Radiomics/pyradiomics,Radiomics/pyradiomics