Save error state in kolab_storage_cache::select() return value

plugins/libkolab/lib/kolab_storage_cache.php

@@ -453,6 +453,7 @@ class kolab_storage_cache
             );
 
             if ($this->db->is_error($sql_result)) {
+                $result->set_error(true);
                 return $result;
             }
 
@@ -483,6 +484,7 @@ class kolab_storage_cache
             }
 
             if ($index->is_error()) {
+                $result->set_error(true);
                 return $result;
             }
 

plugins/libkolab/lib/kolab_storage_dataset.php

@@ -32,6 +32,7 @@ class kolab_storage_dataset implements Iterator, ArrayAccess, Countable
     private $index = array();
     private $data = array();
     private $iteratorkey = 0;
+    private $error = null;
 
     /**
      * Default constructor
@@ -49,6 +50,22 @@ class kolab_storage_dataset implements Iterator, ArrayAccess, Countable
         }
     }
 
+    /**
+     * Return error state
+     */
+    public function is_error()
+    {
+        return !empty($this->error);
+    }
+
+    /**
+     * Set error state
+     */
+    public function set_error($err)
+    {
+        $this->error = $err;
+    }
+
 
     /*** Implement PHP Countable interface ***/