simplification of is empty, see #11

+quantity/Discrete.m

@@ -1635,19 +1635,15 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 			% ISEMPTY checks if the quantity object is empty
 			%   empty = isempty(obj)
 			
-			% check if there is any dimension which is zero
+			% Check if there is any dimension which is zero
 			empty = any(size(obj) == 0);
 			
-			% if the constructor is called without arguments, a
-			% quantity.Discrete is initialized without an initialization of
-			% the grid. Thus, the grid is not a cell:
+			% If the constructor is called without arguments, a
+			% quantity.Discrete is created without an initialization of
+			% the grid. Thus, the quantity is not initialized and empty if
+			% the grid is not a cell.
 			empty = empty || ~iscell(obj(1).grid);
 			
-			% in order to check this for arrays:
-			% scalar and array empty check has to be separated because the 
-			% [obj.grid] does only work in the array case.
-			empty = empty || any(cellfun(@iscell, [obj.grid]));
-			
 		end % isempty()
 		
 		function P = ztzTimes(a, b)