reduce indentation level in PageItem::DrawObj_Pre() by returning when appropriate

git-svn-id: file:///svn/Scribus/trunk/Scribus@19514 11d20701-8431-0410-a711-e3c959e3b870
#12698: Straight Lines are invisible

git-svn-id: file:///svn/Scribus/trunk/Scribus@19515 11d20701-8431-0410-a711-e3c959e3b870