Only clear known users when we had at least one phonebook entry

Signed-off-by: Joas Schilling <coding@schilljs.com>

apps/provisioning_api/lib/Controller/UsersController.php

@@ -240,9 +240,6 @@ class UsersController extends AUserData {
 		$user = $this->userSession->getUser();
 		$knownTo = $user->getUID();
 
-		// Cleanup all previous entries and only allow new matches
-		$this->knownUserService->deleteKnownTo($knownTo);
-
 		$normalizedNumberToKey = [];
 		foreach ($search as $key => $phoneNumbers) {
 			foreach ($phoneNumbers as $phone) {
@@ -263,6 +260,9 @@ class UsersController extends AUserData {
 			return new DataResponse();
 		}
 
+		// Cleanup all previous entries and only allow new matches
+		$this->knownUserService->deleteKnownTo($knownTo);
+
 		$userMatches = $this->accountManager->searchUsers(IAccountManager::PROPERTY_PHONE, $phoneNumbers);
 
 		if (empty($userMatches)) {