Fix chaining withoutPending() with where() (#1457)

At the moment, `where()` cannot be used correctly while using
`withoutPending()`. For example, if we have a single non-pending tenant
in our DB (with ID 'foo'), queries like
`Tenant::withoutPending()->where('id', 'nonexistent')->first()`will
incorrectly return the non-pending tenant ('foo').

This is because `withoutPending()` does
`$builder->whereNull('data->pending_since')->orWhereNull('data')`. These
two aren't grouped, so `withoutPending()->where('id', 'nonexistent')`
basically translates to "WHERE data->pending_since IS NULL **OR (data IS
NULL AND id = 'nonexistent')**". So the query will include all tenants
whose `pending_since` is null (= all non-pending tenants).

Grouping `->whereNull('data->pending_since')->orWhereNull('data')` in a
closure passed to a separate `where()` fixes this issue.

src/Database/Concerns/PendingScope.php

@@ -58,8 +58,10 @@ class PendingScope implements Scope
     {
         $builder->macro('withoutPending', function (Builder $builder) {
             $builder->withoutGlobalScope(static::class)
-                ->whereNull($builder->getModel()->getColumnForQuery('pending_since'))
-                ->orWhereNull($builder->getModel()->getDataColumn());
+                ->where(function (Builder $query) {
+                    $query->whereNull($query->getModel()->getColumnForQuery('pending_since'))
+                        ->orWhereNull($query->getModel()->getDataColumn());
+                });
 
             return $builder;
         });