allow sharing addressbooks with circles

Signed-off-by: Georg Ehrke <developer@georgehrke.com>

apps/dav/lib/CardDAV/CardDavBackend.php

@@ -167,8 +167,10 @@ class CardDavBackend implements BackendInterface, SyncSupport {
 		}
 		$result->closeCursor();
 
-		// query for shared calendars
+		// query for shared addressbooks
 		$principals = $this->principalBackend->getGroupMembership($principalUriOriginal, true);
+		$principals = array_merge($principals, $this->principalBackend->getCircleMembership($principalUriOriginal));
+
 		$principals = array_map(function($principal) {
 			return urldecode($principal);
 		}, $principals);

apps/dav/lib/Connector/Sabre/Principal.php

@@ -426,13 +426,12 @@ class Principal implements BackendInterface {
 	 * @return array
 	 * @throws Exception
 	 */
-	public function getCircleMembership($principal) {
+	public function getCircleMembership($principal):array {
 		if (!\OC::$server->getAppManager()->isEnabledForUser('circles') || !class_exists('\OCA\Circles\ShareByCircleProvider')) {
 			return [];
 		}
 
 		list($prefix, $name) = \Sabre\Uri\split($principal);
-
 		if ($this->hasCircles && $prefix === $this->principalPrefix) {
 			$user = $this->userManager->get($name);
 			if (!$user) {