Refs #4432 Fixing the error in one case (Referrers>Overview / Goals> Overview)

core/DataArray.php

@@ -287,6 +287,12 @@ class DataArray
                 $revenue = round($revenue);
             }
             $values[Metrics::INDEX_REVENUE] = $revenue;
+
+            // if there are no "visit" column, we force one to prevent future complications
+            // eg. This helps the setDefaultColumnsToDisplay() call
+            if(!isset($values[Metrics::INDEX_NB_VISITS])) {
+                $values[Metrics::INDEX_NB_VISITS] = 0;
+            }
         }
     }