COMP: Guard CurvatureRegularizer wrapping on FFTW availability

itkVariationalRegistrationCurvatureRegularizer.h is entirely guarded
by #if defined(ITK_USE_FFTWD) || defined(ITK_USE_FFTWF). When FFTW
is not available the class does not exist, so the wrapping file must
also be conditional. Without this guard, castxml emits:

  error: no template named 'VariationalRegistrationCurvatureRegularizer'
         in namespace 'itk'; did you mean 'VariationalRegistrationRegularizer'?

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hjmjohnson

wrapping/itkVariationalRegistrationCurvatureRegularizer.wrap

@@ -1,7 +1,9 @@
-itk_wrap_class("itk::VariationalRegistrationCurvatureRegularizer" POINTER)
-#  itk_wrap_image_filter("${WRAP_ITK_USIGN_INT}" 2)
-#  itk_wrap_image_filter("${WRAP_ITK_SIGN_INT}" 2)
-  itk_wrap_image_filter("${WRAP_ITK_REAL}" 2)
-  itk_wrap_image_filter("${WRAP_ITK_VECTOR_REAL}" 2)
-  itk_wrap_image_filter("${WRAP_ITK_COV_VECTOR_REAL}" 2)
-itk_end_wrap_class()
+if(ITK_USE_FFTWD OR ITK_USE_FFTWF)
+  itk_wrap_class("itk::VariationalRegistrationCurvatureRegularizer" POINTER)
+  #  itk_wrap_image_filter("${WRAP_ITK_USIGN_INT}" 2)
+  #  itk_wrap_image_filter("${WRAP_ITK_SIGN_INT}" 2)
+    itk_wrap_image_filter("${WRAP_ITK_REAL}" 2)
+    itk_wrap_image_filter("${WRAP_ITK_VECTOR_REAL}" 2)
+    itk_wrap_image_filter("${WRAP_ITK_COV_VECTOR_REAL}" 2)
+  itk_end_wrap_class()
+endif()