[Guided Decision Table] Dragging table should be disabled when pinned

If you enter "pinned mode" it is still possible to drag the table using the "drag handle" (i.e. table name cell). This appears to be caused by GridWidgetDnDMouseMoveHandler.findGridColumn(...) that sets the DnD state to GRID_MOVE_PENDING when over the "drag handle" even if the table is "pinned".

Panning is OK.