COMP: Fix fresh configuration as an ITK module.

On an initial fresh configuration of ITK as a module, ITKConfig.cmake is
not available in the first CMake configuration pass, so return pre-maturely in
this case.

Change-Id: Ia55e9d7c4ca34b1e167bd1408d8afcce0b871b6b
Merge "COMP: Fix fresh configuration as an ITK module."