Make sure we do not return people that we already shared with

We should use the provided list of users and groups that we already
shared with to filter suggestions.

core/ajax/share.php

@@ -241,6 +241,14 @@ if (isset($_POST['action']) && isset($_POST['itemType']) && isset($_POST['itemSo
 					$usergroups = OC_Group::getUserGroups(OC_User::getUser());
 					$groups = array_intersect($groups, $usergroups);
 				}
+
+				$sharedUsers = [];
+				$sharedGroups = [];
+				if (isset($_GET['itemShares'])) {
+					$sharedUsers = isset($_GET['itemShares'][OCP\Share::SHARE_TYPE_USER]) ? $_GET['itemShares'][OCP\Share::SHARE_TYPE_USER] : [];
+					$sharedGroups = isset($_GET['itemShares'][OCP\Share::SHARE_TYPE_GROUP]) ? $_GET['itemShares'][OCP\Share::SHARE_TYPE_GROUP] : [];
+				}
+
 				$count = 0;
 				$users = array();
 				$limit = 0;
@@ -252,8 +260,13 @@ if (isset($_POST['action']) && isset($_POST['itemType']) && isset($_POST['itemSo
 					} else {
 						$users = OC_User::getDisplayNames((string)$_GET['search'], $limit, $offset);
 					}
+
 					$offset += $limit;
 					foreach ($users as $uid => $displayName) {
+						if (in_array($uid, $sharedUsers)) {
+							continue;
+						}
+
 						if ((!isset($_GET['itemShares'])
 							|| !is_array((string)$_GET['itemShares'][OCP\Share::SHARE_TYPE_USER])
 							|| !in_array($uid, (string)$_GET['itemShares'][OCP\Share::SHARE_TYPE_USER]))
@@ -274,6 +287,10 @@ if (isset($_POST['action']) && isset($_POST['itemType']) && isset($_POST['itemSo
 				$l = \OC::$server->getL10N('core');
 
 				foreach ($groups as $group) {
+					if (in_array($group, $sharedGroups)) {
+						continue;
+					}
+
 					if ($count < 15) {
 						if (!isset($_GET['itemShares'])
 							|| !isset($_GET['itemShares'][OCP\Share::SHARE_TYPE_GROUP])