Fixes #3898, fix error that occurs when multi row evolution is called w/o...

Fixes #3898, fix error that occurs when multi row evolution is called w/o labels for periods w/ no data.

plugins/API/API.php

@@ -1197,7 +1197,7 @@ class Piwik_API_API
             }
         }
 
-        if (count($labels) > 1) {
+        if (count($labels) != 1) {
             $data = $this->getMultiRowEvolution(
                 $dataTable,
                 $idSite,
@@ -1538,7 +1538,10 @@ class Piwik_API_API
             }
             
             $newTable = $table->getEmptyClone();
-            $newTable->addRow($newRow);
+            if (!empty($labels)) { // only add a row if the row has data (no labels === no data)
+                $newTable->addRow($newRow);
+            }
+            
             $dataTableMulti->addTable($newTable, $tableLabel);
         }
 

tests/PHPUnit/Integration/RowEvolutionTest.php

@@ -171,6 +171,21 @@ class Test_Piwik_Integration_RowEvolution extends IntegrationTestCase
             )
         ));
         
+        // test multi row evolution when there is no data
+        $return[] = array('API.getRowEvolution', array(
+            'testSuffix'             => '_multiWithNoData',
+            'periods'                => 'day',
+            'idSite'                 => $idSite,
+            'date'                   => $today,
+            'otherRequestParameters' => array(
+                'date'      => '2010-04-01,2010-04-06',
+                'period'    => 'day',
+                'apiModule' => 'Referers',
+                'apiAction' => 'getWebsites',
+                // no label
+            )
+        ));
+        
         // (non-rowevolution test) test flattener w/ search engines to make sure
         // queued filters are not applied twice
         $return[] = array('Referers.getSearchEngines', array(