Reorder some code to skip sorting not preferred tablets when we won't…

… need them

Signed-off-by: Eduardo J. Ortega U <5791035+ejortegau@users.noreply.github.com>

go/vt/vtctl/reparentutil/util.go

@@ -164,15 +164,16 @@ func ElectNewPrimary(
 	if err != nil {
 		return nil, err
 	}
-	err = sortTabletsForReparent(preferNotTablets, preferNotTabletPositions, innodbBufferPool, opts.durability)
-	if err != nil {
-		return nil, err
-	}
 
 	if len(validTablets) > 0 {
 		return validTablets[0].Alias, nil
 	}
 
+	err = sortTabletsForReparent(preferNotTablets, preferNotTabletPositions, innodbBufferPool, opts.durability)
+	if err != nil {
+		return nil, err
+	}
+
 	return preferNotTablets[0].Alias, nil
 }