#12647: fix inconsistent "Low Resolution" enabled with non-Image items

git-svn-id: file:///svn/Scribus/trunk/Scribus@19470 11d20701-8431-0410-a711-e3c959e3b870
#12646: "Update All Marks" crashes Scribus if no document is opened

git-svn-id: file:///svn/Scribus/trunk/Scribus@19472 11d20701-8431-0410-a711-e3c959e3b870