debug: Write exception to log

Signed-off-by: Julius Knorr <[email protected]>

lib/Storage/Storage.php

@@ -458,7 +458,7 @@ public function writeBack($tmpFile, $path) {
 				$this->fileCache->set($serverUrl, ['instance' => $file]);
 			}
 		} catch (\Exception $e) {
-			// noop
+			logger('sharepoint')->error('Failed to write back: ' . $e->getMessage(), ['exception' => $e]);
 		}
 	}