Expose Sheet::isActive() to provide info about the last active sheet (#405)

src/Spout/Reader/CSV/Sheet.php

@@ -32,4 +32,31 @@ class Sheet implements SheetInterface
     {
         return $this->rowIterator;
     }
+
+    /**
+     * @api
+     * @return int Index of the sheet
+     */
+    public function getIndex()
+    {
+        return 0;
+    }
+
+    /**
+     * @api
+     * @return string Name of the sheet - empty string since CSV does not support that
+     */
+    public function getName()
+    {
+        return '';
+    }
+
+    /**
+     * @api
+     * @return bool Always TRUE as there is only one sheet
+     */
+    public function isActive()
+    {
+        return true;
+    }
 }