BUG: Regressions with respect to building DCMTK

1. The wrong hash tag was given to check out DCMTK
from https://github.com/InsightSoftwareConsortium/DCMTK

2. Erroneous conditional inclusion of statements in
Modules/ThirdParty/DCMTK/itk-module-init.cmake

Change-Id: I313bdf5c1b3dacc81a2d8b2f73dd8a9b5ad3e322
Merge topic 'Fix_DCMTK_PATCH_Regression'

31bc608 BUG: Regressions with respect to building DCMTK