set target namespace for diagram type NONE

If the type of the diagram is Bpmn2DiagramType.NONE, no target namespace
is set on the definition, even if it was provided though the editor
input. Definitions without target namespace, cause a validation error
durring the saving of the model.

Signed-off-by: Flavio Donzé <flavio.donze@gmx.ch>
diff --git a/plugins/org.eclipse.bpmn2.modeler.ui/src/org/eclipse/bpmn2/modeler/ui/editor/BPMN2Editor.java b/plugins/org.eclipse.bpmn2.modeler.ui/src/org/eclipse/bpmn2/modeler/ui/editor/BPMN2Editor.java
index 911506f..f903cf6 100644
--- a/plugins/org.eclipse.bpmn2.modeler.ui/src/org/eclipse/bpmn2/modeler/ui/editor/BPMN2Editor.java
+++ b/plugins/org.eclipse.bpmn2.modeler.ui/src/org/eclipse/bpmn2/modeler/ui/editor/BPMN2Editor.java
@@ -388,8 +388,10 @@
 				// If the bpmn file was missing DI elements, they would have been added by the importer
 				// so save the file now in case it was changed.
 				saveModelFile();
+			} else {
+				modelHandler.getDefinitions().setTargetNamespace(targetNamespace);
 			}
-			
+
 			DIImport di = new DIImport(this);
 			di.setModelHandler(modelHandler);