log: modify lock defer unlock order in sync handler (#24667)

This modifies the order of Lock() defer Unlock() to follow the more
typically used pattern.

log/handler.go

@@ -52,8 +52,9 @@ func StreamHandler(wr io.Writer, fmtr Format) Handler {
 func SyncHandler(h Handler) Handler {
 	var mu sync.Mutex
 	return FuncHandler(func(r *Record) error {
-		defer mu.Unlock()
 		mu.Lock()
+		defer mu.Unlock()
+
 		return h.Log(r)
 	})
 }