added two default:break to avoid clang severe warnings

wrap/gl/gl_mesh_attributes_feeder.h

@@ -1279,6 +1279,7 @@ protected:
         {
             break;
         }
+        default : break;
         }
     }
 
@@ -1378,6 +1379,7 @@ protected:
                 else
                     return facenum * cbo._components;
             }
+            default : break;
             }
         }
         catch(std::out_of_range& /*exc*/)