fix conditional expression

bin/account-manager.pl.in

@@ -217,7 +217,7 @@ sub list_providers {
 
     my $providers = IdPAccountManager::Data::ServiceProvider::Manager->get_serviceproviders(db => $db, %args);
 
-    if (@$providers) {
+    if (! @$providers) {
         printf "No service provider in DB\n";
     }