Minor code cleanups in buffer.{cc,hh}

src/buffer.cc

@@ -187,14 +187,7 @@ struct Buffer::Modification
 
     Modification inverse() const
     {
-        Type inverse_type = Insert;
-        switch (type)
-        {
-        case Insert: inverse_type = Erase;  break;
-        case Erase:  inverse_type = Insert; break;
-        default: kak_assert(false);
-        }
-        return {inverse_type, coord, content};
+        return {type == Insert ? Erase : Insert, coord, content};
     }
 };