comment -> issue #820

Device/Detector/Detector2D.cpp

@@ -65,7 +65,7 @@ size_t Detector2D::indexOfSpecular(const Beam& beam) const
     double alpha = beam.alpha_i();
     double phi = beam.phi_i();
     if (alpha + phi < 0)
-        return -1;
+        return -1; // issue #820
     // return getGlobalIndex(
     return totalSize();
 }