[PVR] : 4 fixes related to chanel icons

This pr fixes 4 issues related to  pvr channels icon : 

1) When masterlockcode is set and user click on the logo button in channel manager, the password dialog box is shown twice and user need to enter the password 2 times.
This is resolved by removing and uneeded call to  g_passwordManager.IsMasterLockUnlocked in CGUIDialogPVRChannelManager::OnClickButtonChannelLogo

2)When user set a user defined logo; the iconpath is emptied upon xbmc restart. This is fixed by setting the userseticon flag to true when user choose its own icon.

3) When the icon path  related file does not exists anymore, it should be emptied. This is particulary boring when UserSetIcon is set because it will never been emptied regarding how updatefromclient works. This is fixed by veryfing if the file exists in CPVRChannelGroup::SearchAndSetChannelIcons

4) When user set a custom name for a channel in Channel manager, SearchAndSetChannelIcons should also search for  an icon file based on that name.