fix case empty shot input

matlab/gdat.m

@@ -188,7 +188,7 @@ try
     args = [{shot,data_request},varargin_eff];
   end
   % treat multiple shot numbers
-  if nargin > 0 && isnumeric(shot)
+  if nargin > 0 && isnumeric(shot) && ~isempty(shot)
     args_in = args;
     for i=1:numel(shot)
       args{1} = shot(i);