BUG: Assign Remote modules to groups more robustly.

Since Remote modules are downloaded at configure time, the detected module
name, extracted from the itk-module.cmake file, used to assign to a Group
may not be immediately available, resulting in
errors:

  CMake Error at CMake/ITKGroups.cmake:125 (list):
    list index: 6 out of range (-6, 5)
  Call Stack (most recent call first):
     CMake/ITKModuleEnablement.cmake:93 (include)
     CMakeLists.txt:304 (include)

Switch the order for checking the module name and the presence of the file
itk-module-init.cmake to prevent list access errors.

Change-Id: I28b1139254c046b81d890e13711ef910c304516f
Merge topic 'module-group-count'

9dbb3e58 BUG: Assign Remote modules to groups more robustly.