OC_VCategories: sort categories in natural order using usort

Use usort to sort, so that the json encoding is an array.

lib/vcategories.php

@@ -64,6 +64,7 @@ class OC_VCategories {
 	*/
 	public function categories() {
 		OC_Log::write('core','OC_VCategories::categories: '.print_r($this->categories, true), OC_Log::DEBUG);
+		usort($this->categories, 'strnatcasecmp'); // usort to also renumber the keys
 		return $this->categories;
 	}
 
@@ -96,7 +97,6 @@ class OC_VCategories {
 		}
 		if(count($newones) > 0) {
 			$this->categories = array_merge($this->categories, $newones);
-			natcasesort($this->categories); // Dunno if this is necessary
 			if($sync === true) {
 				$this->save();
 			}
@@ -146,6 +146,7 @@ class OC_VCategories {
 	 * @brief Save the list with categories
 	 */
 	private function save() {
+		usort($this->categories, 'strnatcasecmp'); // usort to also renumber the keys
 		$escaped_categories = serialize($this->categories);
 		OC_Log::write('core','OC_VCategories::save: '.print_r($this->categories, true), OC_Log::DEBUG);
 		OC_Preferences::setValue($this->user, $this->app, self::PREF_CATEGORIES_LABEL, $escaped_categories);