Fix single node CopyRange

Previously there was a restriction for the range to contain at
least two nodes.

Change-Id: Iadf21d3928303c2ab8df0d93dabd969ed1ff7e09
Reviewed-on: https://gerrit.libreoffice.org/10972
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Tested-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
fdo#80926 Don't move anchors of invalid pages

If the anchor is valid, check if its page is valid too,
before moving anchors on view change.

Change-Id: Idffdfdb786cb29a105c06d652e6ad7315abfb4c5
Reviewed-on: https://gerrit.libreoffice.org/10976
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Tested-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>