Fix broken text layout with ShowLineAndParagraphSeparators

Before we add the current cluster we need to check if there's
space for it. Calling checkFullOtherwiseExtend() also has
the side effect of resetting the space data. We would add
the cluster without checking for space when showing separators,
causing broken behavior like we would count the space in the
current item as trailing space, which would make us chop the
end of the string.

Task-number: QTBUG-28832
Change-Id: I8169662218ff6e645575d4e89a57f6b234f3c4cb
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>

src/gui/text/qtextlayout.cpp

@@ -1788,6 +1788,9 @@ void QTextLine::layout_helper(int maxGlyphs)
             if (!line.length && !lbh.tmpData.length)
                 line.setDefaultHeight(eng);
             if (eng->option.flags() & QTextOption::ShowLineAndParagraphSeparators) {
+                if (lbh.checkFullOtherwiseExtend(line))
+                    goto found;
+
                 addNextCluster(lbh.currentPosition, end, lbh.tmpData, lbh.glyphCount,
                                current, lbh.logClusters, lbh.glyphs);
             } else {