Fix support for lock:false in Composer

Author: Seldaek

Diff for: src/Composer/Plugin.php

@@ -452,12 +452,21 @@ private function updateComposerJson(array $missingRequires, bool $sortPackages)
 
     private function updateComposerLock(Composer $composer, IOInterface $io)
     {
+        if ($composer->getConfig()->get('lock') === false) {
+            return;
+        }
+
         $lock = substr(Factory::getComposerFile(), 0, -4).'lock';
         $composerJson = file_get_contents(Factory::getComposerFile());
         $lockFile = new JsonFile($lock, null, $io);
         $locker = ClassDiscovery::safeClassExists(RepositorySet::class)
             ? new Locker($io, $lockFile, $composer->getInstallationManager(), $composerJson)
             : new Locker($io, $lockFile, $composer->getRepositoryManager(), $composer->getInstallationManager(), $composerJson);
+
+        if (!$locker->isLocked()) {
+            return;
+        }
+
         $lockData = $locker->getLockData();
         $lockData['content-hash'] = Locker::getContentHash($composerJson);
         $lockFile->write($lockData);