Remove some duplicate code when setting text edit mode

git-svn-id: file:///svn/Scribus/trunk/Scribus@19501 11d20701-8431-0410-a711-e3c959e3b870
#12680: "Show Baseline Grid" is disabled after enabling/disabling Preview Mode

git-svn-id: file:///svn/Scribus/trunk/Scribus@19502 11d20701-8431-0410-a711-e3c959e3b870