Fix vitessio#16565

This did not have a practical impact but was obviously
wrong

Signed-off-by: Matt Lord <mattalord@gmail.com>

go/vt/vtctl/workflow/materializer.go

@@ -618,7 +618,7 @@ func primaryVindexesDiffer(ms *vtctldatapb.MaterializeSettings, source, target *
 		// If neither source nor target have any vindexes, treat the answer to
 		// the question as trivially false.
 		if len(sColumnVindexes) == 0 && len(tColumnVindexes) == 0 {
-			return true
+			return false
 		}
 
 		sPrimaryVindex := sColumnVindexes[0]