Fix viewcontainers bug and handle unmounted disks better
This MR--which should not be squashed when merging--includes three commits, which do the following:
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Commit 1 fixes a bug in
DolphinMainWindow::viewContainers()
to make it take into consideration split views. -
Commit 2 uses the fixed version of this function to iterate through the window's view containers to find any which would be showing invalid paths after unmounting a mounted disk. This fixes https://bugs.kde.org/show_bug.cgi?id=158934
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Commit 3 uses the fixed version of this function to do essentially the same thing but after session restore, to make sure we don't session-restore a window full of invalid paths if any of them have become invalid during the time between when Dolphin was closed and when it was re-launched. This fixes https://bugs.kde.org/show_bug.cgi?id=427619