fix panic due to empty DestinationRule LoadBalancerPolicy

Signed-off-by: Abirdcfly <fp544037857@gmail.com>

Author: Abirdcfly

pkg/loadbalancer/loadbalancer.go

@@ -775,7 +775,9 @@ func (lb *LoadBalancer) OnDestinationRuleUpdate(oldDr, dr *istioapi.DestinationR
 			delete(lb.policyMap, svcPort)
 		}
 		lb.setLoadBalancerPolicy(dr, policyName, svcPort, state.endpoints)
-		lb.policyMap[svcPort].Update(oldDr, dr)
+		if _, exists := lb.policyMap[svcPort]; exists {
+			lb.policyMap[svcPort].Update(oldDr, dr)
+		}
 		lb.policyMutex.Unlock()
 	}
 }
@@ -815,8 +817,10 @@ func (lb *LoadBalancer) setLoadBalancerPolicy(dr *istioapi.DestinationRule, poli
 }
 
 // TryPickEndpoint try to pick a service endpoint from load-balance strategy.
-func (lb *LoadBalancer) tryPickEndpoint(svcPort proxy.ServicePortName, sessionAffinityEnabled bool, endpoints []string,
-	srcAddr net.Addr, netConn net.Conn, cliReq *http.Request) (string, *http.Request, bool) {
+func (lb *LoadBalancer) tryPickEndpoint(
+	svcPort proxy.ServicePortName, sessionAffinityEnabled bool, endpoints []string,
+	srcAddr net.Addr, netConn net.Conn, cliReq *http.Request,
+) (string, *http.Request, bool) {
 	lb.policyMutex.Lock()
 	defer lb.policyMutex.Unlock()
 
@@ -835,8 +839,10 @@ func (lb *LoadBalancer) tryPickEndpoint(svcPort proxy.ServicePortName, sessionAf
 	return endpoint, req, true
 }
 
-func (lb *LoadBalancer) nextEndpointWithConn(svcPort proxy.ServicePortName, srcAddr net.Addr, sessionAffinityReset bool,
-	netConn net.Conn, cliReq *http.Request) (string, *http.Request, error) {
+func (lb *LoadBalancer) nextEndpointWithConn(
+	svcPort proxy.ServicePortName, srcAddr net.Addr, sessionAffinityReset bool,
+	netConn net.Conn, cliReq *http.Request,
+) (string, *http.Request, error) {
 	// Coarse locking is simple. We can get more fine-grained if/when we
 	// can prove it matters.
 	lb.lock.Lock()
@@ -901,8 +907,10 @@ func (lb *LoadBalancer) nextEndpointWithConn(svcPort proxy.ServicePortName, srcA
 
 // TryConnectEndpoints attempts to connect to the next available endpoint for the given service, cycling
 // through until it is able to successfully connect, or it has tried with all timeouts in EndpointDialTimeouts.
-func (lb *LoadBalancer) TryConnectEndpoints(service proxy.ServicePortName, srcAddr net.Addr, protocol string,
-	netConn net.Conn, cliReq *http.Request) (out net.Conn, err error) {
+func (lb *LoadBalancer) TryConnectEndpoints(
+	service proxy.ServicePortName, srcAddr net.Addr, protocol string,
+	netConn net.Conn, cliReq *http.Request,
+) (out net.Conn, err error) {
 	sessionAffinityReset := false
 	for _, dialTimeout := range userspace.EndpointDialTimeouts {
 		endpoint, req, err := lb.nextEndpointWithConn(service, srcAddr, sessionAffinityReset, netConn, cliReq)