util: storagefile: Clarify docs for '@report_broken' of virStorageFileGetMetadata

virStorageFileGetMetadata does not report error if we can't interrogate
the file somehow. Clarify this in the description of the @report_broken
flag as it implies we should report an error in that case. The problem
is that we don't know whether there's a problem and unfortunately just
offload it to qemu.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/util/virstoragefile.c

@@ -4990,7 +4990,8 @@ virStorageFileGetMetadataRecurse(virStorageSourcePtr src,
  * other non-raw format at will.
  *
  * If @report_broken is true, the whole function fails with a possibly sane
- * error instead of just returning a broken chain.
+ * error instead of just returning a broken chain. Note that the inability for
+ * libvirt to traverse a given source is not considered an error.
  *
  * Caller MUST free result after use via virObjectUnref.
  */