Apply the same zoom clamp to DiagramView::zoom()

DiagramView::zoom() had the same unbounded scale() as the element editor:
a held scroll-wheel zoom could overflow the view transform. Clamp the
resulting scale to [m_min_zoom, m_max_zoom] before applying it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HdWpDp3TrPKbHnv7YUcNJj

sources/diagramview.cpp

@@ -334,6 +334,13 @@ void DiagramView::setSelectionMode()
 */
 void DiagramView::zoom(const qreal zoom_factor)
 {
+	// clamp the resulting scale so a repeated wheel-zoom cannot drive the view
+	// transform to floating-point overflow and crash the editor (issue #798)
+	const qreal target = transform().m11() * zoom_factor;
+	if (target < m_min_zoom || target > m_max_zoom) {
+		return;
+	}
+
 	if (zoom_factor >= 1){
 		scale(zoom_factor, zoom_factor);
 	}

sources/diagramview.h

@@ -103,6 +103,12 @@ class DiagramView : public QGraphicsView
 		bool mustIntegrateTitleBlockTemplate(const TitleBlockTemplateLocation &) const;
 		bool gestures() const;
 
+		/// Lowest and highest allowed value of the view transform scale (m11).
+		/// Prevents wheel-zoom from driving the transform to overflow, which
+		/// crashes the editor (see GitHub issue #798, same class of bug).
+		static constexpr qreal m_min_zoom = 0.01;
+		static constexpr qreal m_max_zoom = 200.0;
+
 	signals:
 			/// Signal emitted after the selection mode changed
 		void modeChanged();