util: storage: Don't leak metadata on repeated calls of virStorageFileGetMetadata

util: storage: Don't leak metadata on repeated calls of virStorageFileGetMetadata

When querying storage metadata after a block job we re-run
virStorageFileGetMetadata on the top level storage file. This means that
the workers (virStorageFileGetMetadataInternal) must not overwrite any
pointers without freeing them.

This was not considered for src->compat and src->features. Fix it and
add a comment mentioning that.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>