[PATCH] virsh-snapshot: Avoid passing NULL to qsort() in virshSnapshotListCollect()

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

If a domain has no snapshots and 'virsh snapshot-list' is called,
this gets all the way down to virshSnapshotListCollect() which
then collects all snapshots (none), and passes them to qsort()
which doesn't like being called with NULL:

  extern void qsort (void *__base, size_t __nmemb, size_t __size,
                     __compar_fn_t __compar) __nonnull ((1, 4));

Resolves: https://gitlab.com/libvirt/libvirt/-/issues/533
Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
---
 tools/virsh-snapshot.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/virsh-snapshot.c b/tools/virsh-snapshot.c
index d7889a38e4..ecb935b2b4 100644
--- a/tools/virsh-snapshot.c
+++ b/tools/virsh-snapshot.c
@@ -1310,9 +1310,11 @@ virshSnapshotListCollect(vshControl *ctl, virDomainPtr dom,
             }
         }
     }
-    if (!(orig_flags & VIR_DOMAIN_SNAPSHOT_LIST_TOPOLOGICAL))
+    if (!(orig_flags & VIR_DOMAIN_SNAPSHOT_LIST_TOPOLOGICAL) &&
+        snaplist->snaps) {
         qsort(snaplist->snaps, snaplist->nsnaps, sizeof(*snaplist->snaps),
               virshSnapSorter);
+    }
     snaplist->nsnaps -= deleted;
 
     ret = g_steal_pointer(&snaplist);
-- 
2.41.0