tdf#130440 only select first page if no other page is selected

Found while implementing the UItest.
See https://gerrit.libreoffice.org/c/core/+/88437
it asserts on line 34 AssertionError: 2 != 1 as the first and
second slides are selected

Change-Id: I249dc0ac6faa55f0f15deedb848beabbc64aeed4
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/88439
Tested-by: Xisco Faulí <xiscofauli@libreoffice.org>
Reviewed-by: Xisco Faulí <xiscofauli@libreoffice.org>
(cherry picked from commit 7ed602a3b8c0ffe922b4f082cd4cdaa5a8f0d64c)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/88404
Reviewed-by: Michael Stahl <michael.stahl@cib.de>
Tested-by: Jenkins
diff --git a/sd/source/ui/slidesorter/controller/SlsSelectionObserver.cxx b/sd/source/ui/slidesorter/controller/SlsSelectionObserver.cxx
index 9eaa7b5..4dc2ac08 100644
--- a/sd/source/ui/slidesorter/controller/SlsSelectionObserver.cxx
+++ b/sd/source/ui/slidesorter/controller/SlsSelectionObserver.cxx
@@ -126,7 +126,7 @@ void SelectionObserver::EndObservation()
    bool bSuccess = mrSlideSorter.GetController().GetFocusManager().SetFocusedPageToCurrentPage();
    // tdf#129346 nothing currently selected, select something, if possible
    // but (tdf#129346) only if setting focus to current page failed
    if (!bSuccess && rSelector.GetPageCount())
    if (!bSuccess && rSelector.GetPageCount() && rSelector.GetSelectedPageCount() == 0)
        rSelector.SelectPage(0);
}