PaintOnTemplateFeature: Fix setupTemplate()

Indicate that template configuration is finished before loading the
template file, so that that function takes care of setting the state
to Loaded on success.
Complements aee1057.
Fixes GH-1830 (Cannot add scribble template).

src/templates/paint_on_template_feature.cpp

@@ -351,6 +351,7 @@ Template* PaintOnTemplateFeature::setupTemplate() const
 		template_image->setTemplateScaleY(1.0/pixel_per_mm);
 		template_image->setTemplateShear(0);
 		template_image->setTemplateRotation(0);
+		template_image->setTemplateState(Template::Unloaded);
 		template_image->loadTemplateFile();
 
 		if (template_image->getTemplateState() != Template::Loaded)