[TD]fix fail on missing base view (#7856)

src/Mod/TechDraw/Gui/TaskProjGroup.cpp

@@ -190,8 +190,10 @@ void TaskProjGroup::viewToggled(bool toggle)
                                 multiView->getNameInDocument(), viewNameCStr);
         changed = true;
     } else if ( !toggle && multiView->hasProjection( viewNameCStr ) ) {
-        multiView->removeProjection( viewNameCStr );
-        changed = true;
+        if (multiView->canDelete(viewNameCStr)) {
+            multiView->removeProjection( viewNameCStr );
+            changed = true;
+        }
     }
     if (changed) {
         if (multiView->ScaleType.isValue("Automatic")) {
@@ -473,6 +475,9 @@ void TaskProjGroup::setupViewCheckboxes(bool addConnections)
         const char *viewStr = viewChkIndexToCStr(i);
         if (viewStr && multiView->hasProjection(viewStr)) {
             box->setCheckState(Qt::Checked);
+            if (!multiView->canDelete(viewStr)) {
+                box->setEnabled(false);
+            }
         } else {
             box->setCheckState(Qt::Unchecked);
         }

src/Mod/TechDraw/Gui/ViewProviderViewPart.cpp

@@ -227,6 +227,10 @@ bool ViewProviderViewPart::setEdit(int ModNum)
     TechDraw::DrawViewPart* dvp = getViewObject();
     TechDraw::DrawViewDetail* dvd = dynamic_cast<TechDraw::DrawViewDetail*>(dvp);
     if (dvd) {
+        if (!dvd->BaseView.getValue()) {
+            Base::Console().Error("DrawViewDetail - %s - has no BaseView!\n", dvd->getNameInDocument());
+            return false;
+        }
         // clear the selection (convenience)
         Gui::Selection().clearSelection();
         Gui::Control().showDialog(new TaskDlgDetail(dvd));