[TD]trap wrong selection for ArchSection

src/Mod/TechDraw/App/DrawViewArch.cpp

@@ -103,6 +103,14 @@ App::DocumentObjectExecReturn *DrawViewArch::execute(void)
     }
 
     App::DocumentObject* sourceObj = Source.getValue();
+    //if (sourceObj is not ArchSection) return
+    App::Property* proxy = sourceObj->getPropertyByName("Proxy");
+    if (proxy == nullptr) {
+        Base::Console().Error("DVA::execute - %s is not an ArchSection\n", sourceObj->Label.getValue());
+        //this is definitely not an ArchSection
+        return DrawView::execute();
+    }
+
     if (sourceObj) {
         std::string svgFrag;
         std::string svgHead = getSVGHead();