Add backwards compatibility with strings

zipmask_pack.m

@@ -24,11 +24,11 @@ if ( length(d_mat) ~= length(d_mask) || ...
 end
 
 if length(d_mat) ~= 3
-    error("Only implemented for 3D arrays, yet");
+    error('Only implemented for 3D arrays, yet');
 end
 
 if all(all(all(mask == 0)))
-    warning("Mask is empty");
+    warning('Mask is empty');
     out.data = [];
     out.mask = [];
     out.dimension = size(matrix);