Small syntax fix

Signed-off-by: Nicola Vigano <nicola.vigano@esrf.fr>

5_reconstruction/GtGuiThresholdGrain.m

@@ -11,10 +11,10 @@ classdef GtGuiThresholdGrain < GtVolView
     methods
         function obj = GtGuiThresholdGrain(vol, varargin)
             viewer_args = varargin;
-            if ~ismember('f_title', varargin(1:2:end))
+            if (~ismember('f_title', varargin(1:2:end)))
                 viewer_args(end+1:end+2) = {'f_title', 'Volume Segmentation'};
             end
-            if ~ismember('overlay', varargin(1:2:end))
+            if (~ismember('overlay', varargin(1:2:end)))
                 viewer_args(end+1:end+2) = {'overlay', vol};
             end