-Werror,-Wimplicit-fallthrough

Change-Id: I13a6a64f118bcfb99f47cd47a0dc638c5c9a5a14

vcl/unx/gtk3/gtk3salnativewidgets-gtk.cxx

@@ -2131,6 +2131,7 @@ bool GtkSalGraphics::drawNativeControl( ControlType nType, ControlPart nPart, co
         }
         Rectangle aRect(Point(nX, nY), Size(nWidth, nHeight));
         render_common(mpNotebookHeaderTabsTabStyle, cr, aRect, flags);
+        break;
     }
     default:
         break;