coverity#1326304 Explicit null dereferenced

Change-Id: I1fba88431ec7e5154f39bb0c76e622c6129011d2

wizards/com/sun/star/wizards/document/GridControl.java

@@ -51,6 +51,12 @@ public class GridControl extends Shape
             xNameAccess = UnoRuntime.queryInterface( XNameAccess.class, oGridModel );
             _xFormName.insertByName(_sname, oGridModel);
             XControlModel xControlModel = UnoRuntime.queryInterface( XControlModel.class, oGridModel );
+            // test if the interface was available
+            if (xControlModel == null) {
+                throw new Exception(
+                    "Error: GridModel does not export XControlModel interface");
+            }
+
             xControlShape.setControl(xControlModel);
             xPropertySet = UnoRuntime.queryInterface( XPropertySet.class, oGridModel );
             oFormHandler.xDrawPage.add(xShape);