patch 9.0.2034: don't try to copy SMACK attribute, when none exist

Problem:  don't try to copy SMACK attribute, when none exist
Solution: return early if SMACK extended attributes do not exist or
          if they are not supported

closes: #1711
closes: #13348

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/os_unix.c b/src/os_unix.c
index 237171b..11448c5 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -3047,6 +3047,11 @@
     if (from_file == NULL)
 	return;
 
+    size = listxattr((char *)from_file, NULL, 0);
+    // not supported or no attributes to copy
+    if (errno == ENOTSUP || size == 0)
+	return;
+
     for (index = 0 ; index < (int)(sizeof(smack_copied_attributes)
 			      / sizeof(smack_copied_attributes)[0]) ; index++)
     {