BUG: Use ProcessObject GetInput to obtain base pointer
BUG: Use ProcessObject GetInput to obtain base pointer

In ImageSinc::GenerateNthInputRequestedRegion, use superclass'
GetInput method to obtain a pointer to a DataObject then a
dynamic_cast can be used to determine if the image region can be
generated. This addresses runtime "Unable to convert input" warnings.

hjmjohnson/ITK,BRAINSia/ITK,InsightSoftwareConsortium/ITK,hjmjohnson/ITK,richardbeare/ITK,BRAINSia/ITK,thewtex/ITK,richardbeare/ITK,BRAINSia/ITK,hjmjohnson/ITK,Kitware/ITK,Kitware/ITK,InsightSoftwareConsortium/ITK,vfonov/ITK,LucasGandel/ITK,richardbeare/ITK,LucasGandel/ITK,InsightSoftwareConsortium/ITK,LucasGandel/ITK,thewtex/ITK,malaterre/ITK,hjmjohnson/ITK,BRAINSia/ITK,Kitware/ITK,vfonov/ITK,vfonov/ITK,richardbeare/ITK,InsightSoftwareConsortium/ITK,Kitware/ITK,richardbeare/ITK,vfonov/ITK,LucasGandel/ITK,malaterre/ITK,malaterre/ITK,vfonov/ITK,malaterre/ITK,InsightSoftwareConsortium/ITK,richardbeare/ITK,LucasGandel/ITK,BRAINSia/ITK,thewtex/ITK,BRAINSia/ITK,Kitware/ITK,malaterre/ITK,vfonov/ITK,thewtex/ITK,thewtex/ITK,Kitware/ITK,thewtex/ITK,BRAINSia/ITK,malaterre/ITK,malaterre/ITK,vfonov/ITK,InsightSoftwareConsortium/ITK,LucasGandel/ITK,thewtex/ITK,vfonov/ITK,Kitware/ITK,vfonov/ITK,malaterre/ITK,InsightSoftwareConsortium/ITK,malaterre/ITK,LucasGandel/ITK,hjmjohnson/ITK,hjmjohnson/ITK,richardbeare/ITK,LucasGandel/ITK,hjmjohnson/ITK