Usability improvement in cases with insufficient access rights to open a document

[variar]

From nickbnf/glogg#291 by @zell-mbc:

Ran into the situation that I wanted to open a log and the app just did nothing, no error. Either opens with a blank screen, or in case Glogg is open already, just nothing. Upon looking into this in more detail it turned out that the user didn't have the necessary rights to open the document. I would suggest presenting an error message in cases like this.

To reproduce:

1. Change access rights on logfile which will prevent user from reading it. chown/chmod
2. File/Open (try)

I would propose an error saying that the file is not readable instead of no visual feedback.