Move PythonQt wrapping option code after ctkMacroValidateBuildOptions

CMake code responsible of exposing the PythonQt wrapping was
included before the invocation of "ctkMacroValidateBuildOptions"

This was leading to an error in case only CTK_LIB_Scripting/Python/Widgets
was enabled.

CMakeLists.txt

@@ -377,24 +377,6 @@ FOREACH(app ${CTK_APPLICATIONS})
 ENDFOREACH()
 
 #-----------------------------------------------------------------------------
-# CTK Python wrapping - Propose the option only if CTK_LIB_Scriping/Python/Core is ON
-IF(CTK_LIB_Scripting/Python/Core)
-  find_package(PythonInterp)
-  IF(NOT PYTHONINTERP_FOUND)
-    MESSAGE(SEND_ERROR "PYTHON_EXECUTABLE not specified or inexistent when CTK_LIB_Scripting is enabled")
-  ENDIF()
-  OPTION(CTK_WRAP_PYTHONQT_FULL "Wrap CTK classes using Qt meta-object system into Python language" OFF)
-  OPTION(CTK_WRAP_PYTHONQT_LIGHT "Wrap CTK classes using Qt meta-object system into Python language" OFF)
-  IF(CTK_WRAP_PYTHONQT_FULL AND CTK_WRAP_PYTHONQT_LIGHT)
-    MESSAGE(SEND_ERROR "CTK_WRAP_PYTHONQT_{LIGHT,FULL} options are mutually exclusive. Please enable only one !")
-  ENDIF()
-ELSE()
-  # Note that an unset boolean variable is considered to be False
-  UNSET(CTK_WRAP_PYTHONQT_FULL CACHE)
-  UNSET(CTK_WRAP_PYTHONQT_LIGHT CACHE)
-ENDIF()
-
-#-----------------------------------------------------------------------------
 # Generate target_directories list - List of directory corresponding to the different
 # libraries, plugins and applications associated with the corresponding option name.
 #
@@ -445,6 +427,24 @@ ctkFunctionGenerateDGraphInput(${CTK_BINARY_DIR} "${target_directories}" FALSE)
 ctkMacroValidateBuildOptions("${CTK_BINARY_DIR}" "${DGraph_EXECUTABLE}" "${target_directories}")
 
 #-----------------------------------------------------------------------------
+# CTK Python wrapping - Propose the option only if CTK_LIB_Scriping/Python/Core is ON
+IF(CTK_LIB_Scripting/Python/Core)
+  find_package(PythonInterp)
+  IF(NOT PYTHONINTERP_FOUND)
+    MESSAGE(SEND_ERROR "PYTHON_EXECUTABLE not specified or inexistent when CTK_LIB_Scripting is enabled")
+  ENDIF()
+  OPTION(CTK_WRAP_PYTHONQT_FULL "Wrap CTK classes using Qt meta-object system into Python language" OFF)
+  OPTION(CTK_WRAP_PYTHONQT_LIGHT "Wrap CTK classes using Qt meta-object system into Python language" OFF)
+  IF(CTK_WRAP_PYTHONQT_FULL AND CTK_WRAP_PYTHONQT_LIGHT)
+    MESSAGE(SEND_ERROR "CTK_WRAP_PYTHONQT_{LIGHT,FULL} options are mutually exclusive. Please enable only one !")
+  ENDIF()
+ELSE()
+  # Note that an unset boolean variable is considered to be False
+  UNSET(CTK_WRAP_PYTHONQT_FULL CACHE)
+  UNSET(CTK_WRAP_PYTHONQT_LIGHT CACHE)
+ENDIF()
+
+#-----------------------------------------------------------------------------
 # DGraph
 #