Add missing undo recording.

This adds a change of the printindex type (with multiple indices) to the undo stack and marks the buffer dirty on that action (bug #8182)

src/insets/InsetIndex.cpp

@@ -496,6 +496,7 @@ void InsetPrintIndex::doDispatch(Cursor & cur, FuncRequest & cmd)
 			cur.noScreenUpdate();
 			break;
 		}
+		cur.recordUndo();
 		setParams(p);
 		break;
 	}