Fix the issue2187

[xauthulei]

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[xauthulei]

I am try to address the issue #2187, @bmpotter , Could you review this here, thanks

[xauthulei]

Review comments from @bmpotter in PR2216 ：

This isn't quite right. The effect of && -d $DIR is that if the user specified -f

flag (which sets DIR) but the specified didn't exist or was a file, it would silently not use it (confusing the user).

You have 2 choices:

1. Just remove && -d $DIR from all of the lines you added it to. This will cause pushd to display an error msg if the directory is not valid.

2. Or do number 1 and add a check in checkPrereqsAndInput that the directory specified is valid, and display an error msg and return exit code 1 if not.

The fact that you didn't catch this problem makes me think you didn't test your code thoroughly enough before submitting the PR. Please test both the good path and the error cases. Thx.