enh(log): use level warning for saving empty docs

Saving an empty document can happen from time to time
but if it happens to often it may indicate some problem.
Keep an eye on these without needing to log all debug things in text.

Signed-off-by: Max <max@nextcloud.com>

Author: max-nextcloud

lib/Service/DocumentService.php

@@ -342,7 +342,7 @@ public function autosave(?File $file, int $documentId, int $version, ?string $au
 		}
 
 		if (empty($autoSaveDocument)) {
-			$this->logger->debug('Saving empty document', [
+			$this->logger->warning('Saving empty document', [
 				'requestVersion' => $version,
 				'requestAutosaveDocument' => $autoSaveDocument,
 				'requestDocumentState' => $documentState,