Use SAL_FALLTHROUGH where intended

As discussed on IRC:
<alg> sberg: intended - double includes the lines from single, aka triple
<alg> sberg: Okay, please add comments there. I was referring to
 FillHatchPrimitive2D::create2DDecomposition where the same switch is used

Change-Id: Ie007bdb54a56ead1b9139451d20f2ea6aa7e6f20

drawinglayer/source/primitive3d/hatchtextureprimitive3d.cxx

@@ -150,6 +150,8 @@ namespace drawinglayer
                                                         fAngle - F_PI4);
 
                                                     aHatch.appendTransformations(aMatrices);
+
+                                                    SAL_FALLTHROUGH;
                                                 }
                                                 case attribute::HATCHSTYLE_DOUBLE:
                                                 {
@@ -161,6 +163,8 @@ namespace drawinglayer
                                                         fAngle - F_PI2);
 
                                                     aHatch.appendTransformations(aMatrices);
+
+                                                    SAL_FALLTHROUGH;
                                                 }
                                                 case attribute::HATCHSTYLE_SINGLE:
                                                 {