[cosmetic] remove duplicate access modifier in CGUIMediaWindow
[pvr] refactor directory path preparation out of Update() method

This fixes an issue where we get an infinity loop cause by a fallback done
in GUIMediaWindow::Update() if GetDirectory() return false. This effects only
some of the PVR related windows, because there we override the directory path
directly within the Update() method and the strDirectory param is discarded.
Merge pull request #5052 from xhaggi/fix-pvr-directory-update-infinity-loop

[pvr] fix: directory update infinity loop if GetDirectory() return false