fix [diagram editor] : fix crash on search and replace widget

Qet crash when double click on an element/text/conductor in the tree
widget of the search and replace widget and the item is deleted from
diagram. (Call of Diagram::showme to a nullptr).

sources/SearchAndReplace/ui/searchandreplacewidget.cpp

@@ -961,21 +961,21 @@ void SearchAndReplaceWidget::on_m_tree_widget_itemDoubleClicked(
 	else if (m_element_hash.keys().contains(item))
 	{
 		QPointer<Element> elmt = m_element_hash.value(item);
-		if (elmt) {
+		if (elmt && elmt->diagram()) {
 			elmt.data()->diagram()->showMe();
 		}
 	}
 	else if (m_text_hash.keys().contains(item))
 	{
 		QPointer<IndependentTextItem> text = m_text_hash.value(item);
-		if (text) {
+		if (text && text->diagram()) {
 			text.data()->diagram()->showMe();
 		}
 	}
 	else if (m_conductor_hash.keys().contains(item))
 	{
 		QPointer<Conductor> cond = m_conductor_hash.value(item);
-		if (cond) {
+		if (cond && cond->diagram()) {
 			cond.data()->diagram()->showMe();
 		}
 	}