Add binary check for mask

zipmask_pack.m

@@ -27,6 +27,10 @@ if length(d_mat) ~= 3
     error('Only implemented for 3D arrays, yet');
 end
 
+if numel(mask) ~= numel(find(mask==0)) + numel(find(mask==1))
+    error('Mask appears to be non-binary');
+end
+
 if all(all(all(mask == 0)))
     warning('Mask is empty');
     out.data = [];