osd/SnapMapper: fix _lookup_purged_snap

We should verify that the snap we are looking for matches the
pool also.
Same as we are checking in OSDMonitor:
ceph@0a48392

Fixes: https://tracker.ceph.com/issues/64347

Signed-off-by: Matan Breizman <[email protected]>

Author: Matan-B

src/osd/SnapMapper.cc

@@ -764,6 +764,10 @@ int SnapMapper::_lookup_purged_snap(
   decode(gotpool, p);
   decode(*begin, p);
   decode(*end, p);
+  if (gotpool != pool) {
+    dout(20) << __func__ << " got wrong pool " << gotpool << dendl;
+    return -ENOENT;
+  }
   if (snap < *begin || snap >= *end) {
     dout(20) << __func__ << " pool " << pool << " snap " << snap
 	     << " found [" << *begin << "," << *end << "), no overlap" << dendl;