BUG: Fixing potential bug on number of layers in dataset

Code/UtilitiesAdapters/OGRAdapters/otbOGRDataSourceWrapper.cxx

@@ -411,8 +411,14 @@ void otb::ogr::DataSource::GetGlobalExtent(double & ulx,
   OGREnvelope sExtent;
   const_iterator lit = this->begin();
   
+  if(lit==this->end())
+    { 
+    itkGenericExceptionMacro(<< "Cannot compute global extent because there are no layers in the DataSource");
+    }
+
     const OGRErr res = lit->ogr().GetExtent(&sExtent,force);
 
+
   if(res!= OGRERR_NONE)
     {
     itkGenericExceptionMacro(<< "Cannot retrieve extent of layer <"