DisplayTopKeywords only shows a single character

[halfdan]

As reported in: http://forum.piwik.org/read.php?5,106526

Example: http://demo.piwik.org/index.php?module=Widgetize&action=iframe&moduleToWidgetize=Referers&actionToWidgetize=getKeywordsForPage&idSite=7&period=day&date=2011-02-15&disableLink=1

[anonymous-matomo-user]

In 6e6a4a2: Properly show keywords in DisplayTopKeywords

fixes #4618