Normalize specular simulation even if no background set

In !1909 (merged), by mistake, specular intensity normalization occurs only when a background is set.

To be backported to r21.1.

Sim/Simulation/SpecularSimulation.cpp

@@ -102,7 +102,10 @@ Datafield SpecularSimulation::packResult()
     }
     if (background())
         for (size_t i = 0; i < m_scan->nScan(); i++)
-            vec[i] = background()->addBackground(vec[i]) / m_scan->intensity();
+            vec[i] = background()->addBackground(vec[i]);
+
+    for (size_t i = 0; i < m_scan->nScan(); i++)
+        vec[i] /= m_scan->intensity();
 
     Datafield data({m_scan->coordinateAxis()->clone()}, vec);
     return {data};