Check resource before closing in encryption wrapper

In case of error there is no guarantee that $source or $target is set or
is a resource when handling an error.

Without this fix, there's a risk that fclose will fail and the actual
exception will not be thrown, making it impossible to find out about the
root cause.

Signed-off-by: Vincent Petry <vincent@nextcloud.com>

Author: PVince81

lib/private/Files/Storage/Wrapper/Encryption.php

@@ -756,8 +756,12 @@ private function copyBetweenStorage(Storage\IStorage $sourceStorage, $sourceInte
 				fclose($source);
 				fclose($target);
 			} catch (\Exception $e) {
-				fclose($source);
-				fclose($target);
+				if (is_resource($source)) {
+					fclose($source);
+				}
+				if (is_resource($target)) {
+					fclose($target);
+				}
 				throw $e;
 			}
 			if ($result) {