PointSymbolEditorWidget: Fix 'Line closed' checkmark

When the 'Line closed' checkmark was set and all lines were removed the
checkbox remained set but became disabled.

src/gui/symbols/point_symbol_editor_widget.cpp

@@ -845,7 +845,11 @@ void PointSymbolEditorWidget::updateCoordsTable()
 		if (num_rows > 0 && path->parts().front().isClosed())
 			--num_rows;
 		if (path->getSymbol()->getType() == Symbol::Line)
+		{
+			const QSignalBlocker blocker(line_closed_check);
+			line_closed_check->setChecked(num_rows > 0 && path->parts().front().isClosed());
 			line_closed_check->setEnabled(num_rows > 0);
+		}
 	}
 
 	coords_table->setRowCount(num_rows);