[TD]guard against font size zero

src/Mod/TechDraw/Gui/QGIViewDimension.cpp

@@ -283,7 +283,7 @@ void QGIViewDimension::updateDim()
 
     QFont font = datumLabel->getFont();
     font.setFamily(QString::fromUtf8(vp->Font.getValue()));
-    int fontSize = QGIView::exactFontSize(vp->Font.getValue(), vp->Fontsize.getValue());
+    int fontSize = QGIView::exactFontSize(vp->Font.getValue(), std::max(1.0, vp->Fontsize.getValue()));
     font.setPixelSize(fontSize);
     datumLabel->setFont(font);
 

src/Mod/TechDraw/Gui/ViewProviderDimension.cpp

@@ -349,3 +349,41 @@ std::vector<App::DocumentObject*> ViewProviderDimension::claimChildren() const
 }
 
 
+void ViewProviderDimension::finishRestoring()
+{
+    fixTextSize();
+    fixArrowSize();
+
+    ViewProviderDrawingView::finishRestoring();
+}
+
+
+void ViewProviderDimension::fixTextSize()
+{
+    App::Document* ourDoc = getDocument()->getDocument();
+    if (checkMiniumumDocumentVersion(ourDoc, 1, 1)) {
+        return;
+    }
+
+    double size = Fontsize.getValue();
+    if (size == 0.0) {
+        size = Preferences::dimFontSizeMM();
+        Fontsize.setValue(size);
+    }
+}
+
+
+void ViewProviderDimension::fixArrowSize()
+{
+    App::Document* ourDoc = getDocument()->getDocument();
+    if (checkMiniumumDocumentVersion(ourDoc, 1, 1)) {
+        return;
+    }
+
+    double size = Arrowsize.getValue();
+    if (size == 0.0) {
+        size = Preferences::dimFontSizeMM();
+        Arrowsize.setValue(size);
+    }
+}
+

src/Mod/TechDraw/Gui/ViewProviderDimension.h

@@ -78,6 +78,7 @@ public:
     bool setEdit(int ModNum) override;
     bool doubleClicked() override;
     bool onDelete(const std::vector<std::string> & parms) override;
+    void finishRestoring() override;
 
 
     TechDraw::DrawViewDimension* getViewObject() const override;
@@ -93,6 +94,8 @@ public:
 
     std::vector<App::DocumentObject*> claimChildren() const override;
 
+    void fixTextSize();
+    void fixArrowSize();
 
 protected:
     void handleChangedPropertyType(Base::XMLReader &reader, const char *TypeName, App::Property * prop) override;