Do we need to load all packages each times with providers enabled ?

Hello,
On BuildCommand if we have a package/repository filter, we load all packages to dump them with the PackagesBuilder :
```
if ($packageSelection->hasFilterForPackages() || $packageSelection->hasRepositoryFilter()) {
// in case of an active filter we need to load the dumped packages.json and merge the
// updated packages in
$oldPackages = $packageSelection->load();
$packages += $oldPackages;
ksort($packages);
}

$packagesBuilder = new PackagesBuilder($output, $outputDir, $config, $skipErrors);
$packagesBuilder->dump($packages);
```

Is it really needed if providers option is enabled ?
If no, I can create a pull request to change the code