BUG: Support color DICOM data series (Slicer#7089)

Without this change the vtkITK code complained that a series of
color dicom data could not be loaded.

It appears that when the check for grayscale was added it was only
tested on single instance files, not on series in multiple files.

This change invokes the correct reader based on whether it's a single
file or not.

Modules/Scripted/DICOMPlugins/DICOMScalarVolumePlugin.py

@@ -380,7 +380,10 @@ def loadFilesWithSeriesReader(self, imageIOName, files, name, grayscale=True):
         if grayscale:
             reader = vtkITK.vtkITKArchetypeImageSeriesScalarReader()
         else:
-            reader = vtkITK.vtkITKArchetypeImageSeriesVectorReaderFile()
+            if len(files) > 1:
+                reader = vtkITK.vtkITKArchetypeImageSeriesVectorReaderSeries()
+            else:
+                reader = vtkITK.vtkITKArchetypeImageSeriesVectorReaderFile()
         reader.SetArchetype(files[0])
         for f in files:
             reader.AddFileName(f)