N°686 - protect the edition of dashboards against a no-longer-existing class.

git-svn-id: http://svn.code.sf.net/p/itop/code/trunk@4655 a333f486-631f-4898-b8df-5754b55c2be0

application/dashlet.class.inc.php

@@ -530,7 +530,7 @@ abstract class DashletGroupBy extends Dashlet
 			$this->sGroupByAttCode = $sGroupBy;
 			$this->sFunction = null;
 		}
-		if ($this->oModelReflection->IsValidAttCode($sClass, $this->sGroupByAttCode))
+		if (($sClass != '') && $this->oModelReflection->IsValidAttCode($sClass, $this->sGroupByAttCode))
 		{
 			$sAttLabel = $this->oModelReflection->GetLabel($sClass, $this->sGroupByAttCode);
 			if (!is_null($this->sFunction))