Fix issue 718 -- `display`

[teddychao]

Fixes #718

Cause of the issue

The issue happened at line 32 in pspm_display. This is a line that is iteratively used when pspm_display is running. Initially, the varargin is set to be the input of pspm_display. In default, varargin is empty, so the line is not actually executed. In the next iteration, varargin becomes a multi-cell cell array, which is when nargin is no longer 0. This will not consider the situation that pspm_display actually has an input. I am not fully clear what gui_State.gui_Callback is used for, since it is not really called much in this function. Therefore, I set a situation to identify whether it is processing the user's input as varargin, and this situation is determined in line 38 of the new version.

Changes proposed in this pull request:

• This pull request updates the checking of input variable for display. If the varargin{1} refers to user's input, as a file name or a file path, it will no longer call str2func. The situation for determining the input is a file name or a file path is that the varargin{1} ends with .mat.

[teddychao]

It works now. The UI is ugly. I need to make a new pull request for the UI.