qga: Fix VSS provider GetSnapshotProperties return value

GetSnapshotProperties() returned VSS_E_OBJECT_NOT_FOUND causing
"Snapshot id not found" errors during VSS operations.

Any error in this function causes a similar error in Windows VSS,
so we must return S_OK there.

Signed-off-by: Elizabeth Ashurov <eashurov@redhat.com>
Reviewed-by: Kostiantyn Kostiuk <kkostiuk@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20260211101744.757548-2-eashurov@redhat.com
Signed-off-by: Kostiantyn Kostiuk <kkostiuk@redhat.com>

qga/vss-win32/provider.cpp

@@ -263,7 +263,7 @@ STDMETHODIMP CQGAVssProvider::SetContext(LONG lContext)
 STDMETHODIMP CQGAVssProvider::GetSnapshotProperties(
     VSS_ID SnapshotId, VSS_SNAPSHOT_PROP *pProp)
 {
-    return VSS_E_OBJECT_NOT_FOUND;
+    return S_OK;
 }
 
 STDMETHODIMP CQGAVssProvider::Query(